DOC: Validator + converting array_like to array-like in docstrings
- [ ] closes #40560 (Pending feedback on decorator-generated docstrings)
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

First try at any open source stuff! This one looked pretty doable, hopefully it's there's nothing wrong with it/let me know!
I'm not sure whether *I* should be checking these boxes, or a reviewer should. I *believe* this fixes the issue since it adds the validator, though it's not a particularly clever validator.

It technically is an added test, and it technically works - I re-added one of the entries and got a successful (correct) result for its failure... (amongst the infinite other validation failures 😢 )
I assume linting will run after the PR is submitted, but I'll look into running it locally, too.

```
...
None:None:ES01:pandas.IndexSlice:No extended summary foundNone:None:EX03:pandas.IndexSlice:flake8 error: E231 missing whitespace after ',' (4 times)
.../pandas/pandas/core/indexes/multi.py:434:ES01:pandas.MultiIndex.from_arrays:No extended summary found
.../pandas/pandas/core/indexes/multi.py:434:GL05:pandas.MultiIndex.from_arrays:Use 'array-like' rather than 'array_like' in docstrings.  <<<--- Message for added issue.
.../pandas/pandas/core/indexes/multi.py:500:ES01:pandas.MultiIndex.from_tuples:No extended summary found
.../pandas/pandas/core/indexes/multi.py:567:ES01:pandas.MultiIndex.from_product:No extended summary found
None:None:ES01:pandas.MultiIndex.names:No extended summary found
...
```

More on the validator:
* I chose `GL` as the code after looking through [the numpy docstring validation guide](https://numpydoc.readthedocs.io/en/latest/validation.html) and the [pandas docstring validation guide](https://pandas.pydata.org/docs/dev/development/contributing_docstring.html) - I think it stands for "General" and that seems like the best categorization for this message.
* I used `raw_doc` for this but there was another property like `clean_doc` as well. I could just iterate through each section, too. 🤷 
* I didn't add any extra detail/context to the error message. The line and file are already given, so I think there's nothing extra that's needed.

Using the validator to pick up any missed docstring changes:
```
$ time ./validate_docstrings.py 2>&1 | tee validate_docstrings.log  ### (It takes ~5m to run)
$ grep GL05 validate_docstrings.log
.../pandas/pandas/core/frame.py:10220:GL05:pandas.DataFrame.resample:Use 'array-like' rather than 'array_like' in docstrings.
.../pandas/pandas/core/series.py:5171:GL05:pandas.Series.resample:Use 'array-like' rather than 'array_like' in docstrings.
```

-----

Actually, looking into those two remaining results - those are docstrings generated by lines like:
```10220     @doc(NDFrame.resample, **_shared_doc_kwargs)```

Looking in more detail, I'm not exactly sure how this happens, but it seems like this decorator must be generating text with "array_like" in it. I kind of want to declare it out of scope for this PR, but I can dig into it more if needed.

I suspect maybe the `Substitution` decorator tool can help, possibly. It seems kind of cheesy to add something that will substitute array_like for array-like in a docstring - eg, it might be the result of a function whose param is actually called `array_like`, which, I'm pretty sure they *do* exist. I'm open to feedback on that.

Hi @kemcbride - solid effort here, nice!  I'll take a close look later in the week > So, the check should probably exclude examples

Or just use a different variable name in the example Nice, thanks for updating! From a quick look it looks good, will check again at the weekend Boom. I think this is it!
It took me a while to figure out how to run the `pytest` command on `scripts` dir to actually get the tests to run, but some googling/seeing past PRs helped out there.

Looks like I only needed to fix the one use of `array_like` in core/generic.py to resolve both of the examples issues.

Re-running the validator thing, using the script that's used for ci: https://gist.github.com/kemcbride/0f769423475aeb3aa4f92122cb307cdd, Looks good, return code = 0

Running the validator tests:  https://gist.github.com/kemcbride/93adecdef7717fd0d4ceb689e87775ee

Thanks for the quick review!

 Pinging just as a reminder @MarcoGorelli  Hey @kemcbride - I'm a bit busy ATM with trying to get some things in to 1.3, as that's probably the last minor version before 2.0 and so that last chance for a while (2 years, maybe) to get some deprecations in, mind if I come back to this once 1.3 is in? Should just be a few weeks at most urgh. @MarcoGorelli please don't merge to master ah so sorry @simonjayhawkins - shall I revert these? I don't think that will make much difference. may need to start again as we have a commit for the release and a commit for the new tag and I doubt these will now push to master. These are created locally and only pushed once tests and checks on the documentation build have completed. normally need a 1-2 hour window with no commits to master.

We could maybe change the scripts to not created the commits, and manually tag the hash where we want to branch and then manually tag the first commit after with the dev tag.

The sdist has been built on a tagged branch with an extra commit, but that shouldn't matter for the sdist. Ouch... 

> normally need a 1-2 hour window with no commits to master.

OK, this was completely my fault, but for next time could there be a group mention somewhere advising to not merge anything? I won't make this mistake again, but if any new committers are added there's a risk they might

For what it's worth, I'm free most of today to help out with anything if needed, though I understand there's probably not much I could do here at this point > OK, this was completely my fault,

no worries. vary rarely goes smoothly.

> but for next time could there be a group mention somewhere

That's my fault. I didn't realize i'd left the group mention out of the 1.3 RLS issue. (and I've done the same for 1.4) so that core/triage would get the notifications.  > For what it's worth, I'm free most of today to help out with anything if needed, though I understand there's probably not much I could do here at this point

Thanks. It might get messy when we get to the conda stage. I might need help on that. @MarcoGorelli when merging PRs that close issues can you also add the milestone to the closed issue.