[Release] Update version to 9.5.5

[elastic-vault-github-plugin-prod]

Updates references to the new release 9.5.5.

Merge after the release 9.5.4.

[mergify]

This pull request is now in conflicts. Could you fix it @elastic-vault-github-plugin-prod[bot]? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b update-version-next-9.5.5 upstream/update-version-next-9.5.5
git merge upstream/9.5
git push upstream update-version-next-9.5.5