doc: publish the graphics enablement doc on rtd (#3334)

## What's new?
- Transferred the Mir bringup guide to a how-to guide in the Mir project
- Rewrote the document with a focus on `graphics-core22`. @RAOF please
let me know if any of my assumptions about `graphics-core22` were
incorrect here, since the original document was intended for
`graphics-core20`
- Published the document on readthedocs

## How to test?
- Open the file in CI