Embed Command Palette into xanadu-sphinx-theme w/ enable flag

[Alan-eMartin]

Context:

• Embedded pennylane-command-palette for global search interface.

Description of the Change:

• Embedded production script for pennylane-command-palette.
• Created mobile and desktop button for opening pennylane-command-palette.
• Created event listener for closing, and function for opening command palette.
• Created OS detection logic using navigator and dynamic command label logic.
• Created theme configuration for enabling and disabling the command palette.

Benefits:

• Enables global search of PennyLane content from docs site

Possible Drawbacks:

• None

Related GitHub Issues:

• None

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name and GitHub username in the contributors section.

[AndrewGardhouse]

Code looks great, just one comment:
Is it possible to remove the focus state from here, so it's consistent with pennylane.ai?

[Alan-eMartin]

Done! Thanks for the thorough review @AndrewGardhouse, the PR is now ready for re-review. Sometimes you may need to clear your cache to see changes.

[AndrewGardhouse]

LGTM!