feat: updating to RHDS + several other updates

[markcaron]

• Updated site with RHDS and new design standards
• Updated templates with partials
• Updated README with modified local dev process (to handle CDN env)
• Removed Sass and replaced with modern CSS
• Cleaned up JS functionality on table search
• Added color scheme toggle (e.g., dark mode) and tweaked hero graphic and logos to toggle with color-scheme.
• Made some accessibility improvement all around

Testing instructions

1. Pull down branch
2. Run locally $ zola --config config.dev.toml serve
3. Test on localhost:1111 (per README)

Browser requirements (for page updates)

Your updates should work in the following environments:

• Latest 2 versions of Edge
• Internet Explorer 11 (should be usable, not pixel perfect)
• Latest 2 versions of Firefox (one on macOS, one of Windows OS)
• Firefox 68 (or latest version for Red Hat Enterprise Linux distribution)
• Latest 2 versions of Chrome (one on macOS, one of Windows OS)
• Latest 2 versions of Safari
• Android mobile device (such as the Galaxy S9)
• Apple mobile device (such as the iPhone X)
• Apple tablet device (such as the iPhone Pro)

Ready-for-merge Checklist

Check off items as they are completed. Feel free to delete items if they are not applicable.

• Expected files: all files in this pull request are related to one request or issue (no stragglers or scope-creep).
• Browser testing passed.
• Repository compiles.
• Documentation (README.md, etc.) updated or added.
• Approved by designer or writer (if applicable).

Merging

Please squash when merging and ensure your commit message uses conventional commit formatting.