Update docs for v8

[delvedor]

As titled.

[stale]

We understand that this might be important for you, but this issue has been automatically marked as stale because it has not had recent activity either from our end or yours.
It will be closed if no further activity occurs, please write a comment if you would like to keep this going.

Note: in the past months we have built a new client, that has just landed in master. If you want to open an issue or a pr for the legacy client, you should do that in https://github.com/elastic/elasticsearch-js-legacy

[github-actions]

The backport to 8.0 failed:

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

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-8.0 8.0
# Navigate to the new working tree
cd .worktrees/backport-8.0
# Create a new branch
git switch --create backport-1572-to-8.0
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick --mainline 1 759138c3751baa939f74b620274f2d46d60120fc
# Push it to GitHub
git push --set-upstream origin backport-1572-to-8.0
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.0

Then, create a pull request where the base branch is 8.0 and the compare/head branch is backport-1572-to-8.0.