Add deprecation notes to pandas methods

[phofl]

We have a couple of methods that we want to deprecate right now:

• DEPR: Deprecate Series.ravel pandas-dev/pandas#52511
• DEPR: Series.view pandas-dev/pandas#20251
• Deprecate Index.ravel

You can follow the work that was done in this PR: pandas-dev/pandas#51960

[JustinReboullot]

take

[marechaux]

take with @JustinReboullot

[noatamir]

@JustinReboullot @marechaux which of these are you doing? It would be helpful to know, so others can work on other methods ;)

[marechaux]

We took both, our first PR is here : pandas-dev/pandas#52722

[marechaux]

@JustinReboullot is doing the other currently