Add support for auto-applying light or dark theme

[josh-wong]

Description

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This PR adds support for automatically applying the light or dark theme based on the user's system preference.

Related issues and/or PRs

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N/A

Changes made

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• Added a configuration for automatically applying a theme that matches the user's system preferences based on the configurations in the Docusaurus documentation for color modes.

Checklist

The following is a best-effort checklist. If any items in this checklist are not applicable to this PR, add N/A after each item.

Documentation

• [ ] I have updated the side navigation as necessary. N/A
• [ ] I have updated the documentation to reflect the changes. N/A
• [ ] I have documented or updated any remaining open issues linked to this PR in GitHub, Obsidian, etc. N/A

Build, deploy, and test

• [ ] I have merged and published any dependent changes in other PRs. N/A
• [ ] I have commented my code, particularly in hard-to-understand areas. N/A
• [x] I have checked that my changes look as expected on a locally built version of the docs site.
• [x] My changes generate no new warnings.