Create outline for MM architecture documentation

This issue is for creating the outline of what would need to go into the the MetaMask Architecture document.

When creating the outline please see the comment from [Mark on Issue 27](https://github.com/MetaMask/contributor-docs/issues/27#issuecomment-1739631481)

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 with Mark's comment on Issue 27, then draft the MetaMask Architecture documentation outline from the areas identified there. Get team feedback to finalize the outline, create a pointed issue for each area, and add those tickets to the epic; completion means the outline is agreed and the follow-up issues are created and linked.

Written by the indexing model from the issue text.