[feat]: add supporting components for docs

[zeroedin]

Need supporting components for docs, much like uxdot-*.

We should build some of these components as first-class citizens that will be reused across our docs sites. The caveat to this is supporting the software lifecycle, releases, etc. Considerations should be made for these components which become actively used and dependencies across multiple sites.

Components I believe that could migrate from uxdot-* to rhx-* are:

• rhx-masthead
• rhx-example
• rhx-best-practice
• rhx-copy-permalink
• rhx-copy-button