Fixed Metadata Propogation in DataFrame
In reference to #28283 

Added finalize reference to append, merge, eval, diff, applymap, and update. Removed the ignore marks from the associated tests. 

Hello @jwhitty32! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:







There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-11-04 15:29:31 UTC I'm still failing some checks. Didn't realize committing again in my branch would affect the PR. Sorry! New to this and trying to figure things out. > I'm still failing some checks. Didn't realize committing again in my branch would affect the PR. Sorry! New to this and trying to figure things out.

I think those are related to the change you made to eval Ok, I decided the issue with eval is pretty involved so I will take it off this PR. Going to come back to it in a new one.  Great! Just pushed with merge removed.  thanks @jwhitty32 very nice Sorry to ask a stupid question for this PR. I'm using pandas=1.2.4 and I think that the pd.merge should now propagate the metadata.

```
>>> import pandas
>>> df1 = pandas.DataFrame({"a": [1]})
>>> df1.attrs = {"test": "test"}
>>> df2 = pandas.DataFrame({"a": [1]})
>>> df2.attrs = {"test": "test"}
>>> pandas.merge(df1, df2).attrs
{}
```

I wonder if this is expected? Thank you.