[8.x] (Docs) Add Kibana upgrade notes page (#193268) (#195207)

# Backport

This will backport the following commits from `main` to `8.x`:
- [(Docs) Add Kibana upgrade notes page
(#193268)](#193268)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT
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Add Kibana upgrade notes page (#193268)\n\n## Summary\r\n\r\nThis
PR:\r\n\r\n- adds a page that is a compiled list of all breaking changes
and\r\ndeprecations introduced since the last major version. I slightly
edited\r\nsome bits to align the wording and add version information to
each item,\r\nand took a bit of freedom (not too much!) to ignore items
that shouldn't\r\nbe identified as deprecations or breaking changes, or
to move them to\r\nthe appropriate section in this page.\r\n- adds a
link to the new page from the Upgrade Kibana page.\r\n\r\n<img
width=\"1483\"
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wondering if we should leave this uncategorized or at least
identify\r\nwhich items are specific to a solution. It also doesn't make
much sense\r\nthat we have Obs here while we don't have Security. Let's
think about a\r\nconsistent way to do it.\r\n\r\nNote: In this PR, the
page is initially added under the Release notes\r\nsection. I'll need to
make sure that this does not interfere with the\r\nrelease notes
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automate.\r\n\r\nCloses:
https://github.com/elastic/kibana-team/issues/1075\r\n\r\n---------\r\n\r\nCo-authored-by:
Lisa Cawley <[email protected]>\r\nCo-authored-by: Kaarina Tungseth
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Add Kibana upgrade notes page (#193268)\n\n## Summary\r\n\r\nThis
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and\r\ndeprecations introduced since the last major version. I slightly
edited\r\nsome bits to align the wording and add version information to
each item,\r\nand took a bit of freedom (not too much!) to ignore items
that shouldn't\r\nbe identified as deprecations or breaking changes, or
to move them to\r\nthe appropriate section in this page.\r\n- adds a
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wondering if we should leave this uncategorized or at least
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think about a\r\nconsistent way to do it.\r\n\r\nNote: In this PR, the
page is initially added under the Release notes\r\nsection. I'll need to
make sure that this does not interfere with the\r\nrelease notes
automation.\r\n\r\nNote 2: If we move forward with this proposal, we'll
need update the\r\nrelease notes internal docs to add the relevant
information to this page\r\nwith each minor release, or find a way to
automate.\r\n\r\nCloses:
https://github.com/elastic/kibana-team/issues/1075\r\n\r\n---------\r\n\r\nCo-authored-by:
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Add Kibana upgrade notes page (#193268)\n\n## Summary\r\n\r\nThis
PR:\r\n\r\n- adds a page that is a compiled list of all breaking changes
and\r\ndeprecations introduced since the last major version. I slightly
edited\r\nsome bits to align the wording and add version information to
each item,\r\nand took a bit of freedom (not too much!) to ignore items
that shouldn't\r\nbe identified as deprecations or breaking changes, or
to move them to\r\nthe appropriate section in this page.\r\n- adds a
link to the new page from the Upgrade Kibana page.\r\n\r\n<img
width=\"1483\"
alt=\"image\"\r\nsrc=\"https://github.com/user-attachments/assets/16109072-d5c6-4eb4-8a52-ef209a07072a\">\r\n\r\n<img
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alt=\"image\"\r\nsrc=\"https://github.com/user-attachments/assets/939e9212-b750-4a6f-bd8f-f8df04e46d76\">\r\n\r\n\r\nI'm
wondering if we should leave this uncategorized or at least
identify\r\nwhich items are specific to a solution. It also doesn't make
much sense\r\nthat we have Obs here while we don't have Security. Let's
think about a\r\nconsistent way to do it.\r\n\r\nNote: In this PR, the
page is initially added under the Release notes\r\nsection. I'll need to
make sure that this does not interfere with the\r\nrelease notes
automation.\r\n\r\nNote 2: If we move forward with this proposal, we'll
need update the\r\nrelease notes internal docs to add the relevant
information to this page\r\nwith each minor release, or find a way to
automate.\r\n\r\nCloses:
https://github.com/elastic/kibana-team/issues/1075\r\n\r\n---------\r\n\r\nCo-authored-by:
Lisa Cawley <[email protected]>\r\nCo-authored-by: Kaarina Tungseth
<[email protected]>\r\nCo-authored-by: Luke Elmers
<[email protected]>","sha":"94caafd57d8fcff310ca4117cbf984bbb54658cb"}},{"branch":"8.x","label":"v8.16.0","branchLabelMappingKey":"^v8.16.0$","isSourceBranch":false,"state":"NOT_CREATED"}]}]
BACKPORT-->

Co-authored-by: florent-leborgne <[email protected]>