String dtype: deprecate the pyarrow_numpy storage option
xref https://github.com/pandas-dev/pandas/issues/54792

This old string alias `"string[pyarrow_numpy]"` is being deprecated for just `"str"` or the explicit `pd.StringDtype("pyarrow", na_value=np.nan)`

Directly using FutureWarning (it was an experimental opt-in, so not many people will already have been using it, and then we can directly remove it in pandas 3.0)
Thanks @jorisvandenbossche  Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
git checkout 2.3.x
git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
git cherry-pick -x -m1 1908f2eb962e5c8b84483a6f0582b5e32b6f0ee8
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
git commit -am 'Backport PR #60152: String dtype: deprecate the pyarrow_numpy storage option'
```

4. Push to a named branch:

```
git push YOURFORK 2.3.x:auto-backport-of-pr-60152-on-2.3.x
```

5. Create a PR against branch 2.3.x, I would have named this PR:

> "Backport PR #60152 on branch 2.3.x (String dtype: deprecate the pyarrow_numpy storage option)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the `Still Needs Manual Backport` label once the PR gets merged.

If these instructions are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 Manual backport -> https://github.com/pandas-dev/pandas/pull/60173