Create outline for documentation around the core monorepo

This issue is for creating the outline of what would need to go into the contributor documenation around the the architecture of the core monorepo.

Please use the epic for inspiration on what to include here. [Epic 1588](https://github.com/MetaMask/core/issues/1588)

As part of this work please get feedback from team to finalize the outline and then create issues for filling in each of the areas of the outline. Please add the tickets to the epic and ensure they are pointed.

Start by reviewing Epic 1588 for the architecture topics to include in the contributor documentation outline. Seek team feedback to finalize the outline, then create an issue for each area, add those tickets to the epic, and ensure they are pointed. There are no files or tests named in the issue.

Written by the indexing model from the issue text.