(Docs) Add Kibana upgrade notes page (#193268)

## Summary

This PR:

- adds a page that is a compiled list of all breaking changes and
deprecations introduced since the last major version. I slightly edited
some bits to align the wording and add version information to each item,
and took a bit of freedom (not too much!) to ignore items that shouldn't
be identified as deprecations or breaking changes, or to move them to
the appropriate section in this page.
- adds a link to the new page from the Upgrade Kibana page.

<img width="1483" alt="image"
src="https://github.com/user-attachments/assets/16109072-d5c6-4eb4-8a52-ef209a07072a">

<img width="810" alt="image"
src="https://github.com/user-attachments/assets/939e9212-b750-4a6f-bd8f-f8df04e46d76">


I'm wondering if we should leave this uncategorized or at least identify
which items are specific to a solution. It also doesn't make much sense
that we have Obs here while we don't have Security. Let's think about a
consistent way to do it.

Note: In this PR, the page is initially added under the Release notes
section. I'll need to make sure that this does not interfere with the
release notes automation.

Note 2: If we move forward with this proposal, we'll need update the
release notes internal docs to add the relevant information to this page
with each minor release, or find a way to automate.

Closes: elastic/kibana-team#1075

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Co-authored-by: Lisa Cawley <[email protected]>
Co-authored-by: Kaarina Tungseth <[email protected]>
Co-authored-by: Luke Elmers <[email protected]>