[Release] Update docs for the 8.17.0 release

[elastic-vault-github-plugin-prod]

Update the docs for next minor 8.17.0.

Merge after the release branch for 8.15.2 is created.

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @elastic-vault-github-plugin-prod[bot]? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[ycombinator]

Replaced by #41267 because base branch on this PR is incorrect.