CleanUp AuthenticationService

[froemken]

Before patching #5745 I prefer to cleanup that part in docs first.

[github-actions]

The backport to 12.4 failed:

The process '/usr/bin/git' failed with exit code 1

stderr

error: could not apply 6c433f3aa... CleanUp AuthenticationService
hint: After resolving the conflicts, mark them with
hint: "git add/rm <pathspec>", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".
hint: Disable this message with "git config set advice.mergeConflict false"

stdout

CONFLICT (modify/delete): Documentation/ApiOverview/Authentication/AuthenticationService/Index.rst deleted in HEAD and modified in 6c433f3aa (CleanUp AuthenticationService).  Version 6c433f3aa (CleanUp AuthenticationService) of Documentation/ApiOverview/Authentication/AuthenticationService/Index.rst left in tree.

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-12.4 12.4
# Navigate to the new working tree
cd .worktrees/backport-12.4
# Create a new branch
git switch --create backport-5762-to-12.4
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick 6c433f3aae2849529004bda812711121ff74d5df
# Push it to GitHub
git push --set-upstream origin backport-5762-to-12.4
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-12.4

Then, create a pull request where the base branch is 12.4 and the compare/head branch is backport-5762-to-12.4.