Add test to verify default node filter function

[JoshMock]

Turns out elastic/elastic-transport-js#231 doesn't require any actual fix in the client! Adding a test and updating docs anyway.

[JoshMock]

Tests will fail until the next transport patch release goes out.

[github-actions]

The backport to 8.x 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.x 8.x
# Navigate to the new working tree
cd .worktrees/backport-8.x
# Create a new branch
git switch --create backport-2756-to-8.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 98b38028aa7b93cb14aa52e67c8e0bf2bbaf45af
# Push it to GitHub
git push --set-upstream origin backport-2756-to-8.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.x

Then, create a pull request where the base branch is 8.x and the compare/head branch is backport-2756-to-8.x.