add readthedocs content to the guide

[miguelgrinberg]

This change adds content only available in the readthedocs documentation to the Python client guide hosted on elastic.co.

• new section on using asyncio with the Python Elasticsearch client
• additional examples hosted on the elasticsearch-labs repo as notebooks
• minor additions and improvements to the getting started page

[github-actions]

A documentation preview will be available soon.

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• 📚 HTML diff
• 📙 Preview page

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[pquentin]

Excellent work,thank you! Can we easily add a sample code snippet to the index page?

[pquentin]

Thanks! LGTM.

[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-2769-to-8.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 03033cc60ee3ce9d563e8db772b3e6c0e7d7c87c
# Push it to GitHub
git push --set-upstream origin backport-2769-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-2769-to-8.x.

[github-actions]

The backport to 8.18 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-8.18 8.18
# Navigate to the new working tree
cd .worktrees/backport-8.18
# Create a new branch
git switch --create backport-2769-to-8.18
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 03033cc60ee3ce9d563e8db772b3e6c0e7d7c87c
# Push it to GitHub
git push --set-upstream origin backport-2769-to-8.18
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.18

Then, create a pull request where the base branch is 8.18 and the compare/head branch is backport-2769-to-8.18.