Clarify + Expand on maintainers.md

[cicoyle]

1. We should expand this maintainers doc to say who is a maintainer for what repo.
2. We should also add an approvers.md file to note who is an approver for what repo.

[msfussell]

For 1 and 2 these are all listed in the Project Teams listed here https://github.com/orgs/dapr/teams. Otherwise it makes it hard to continuously update this file and keep it accurate

[cicoyle]

Fair, as a compromise, how about we link from inside the maintainers markdown file that teams link? That way we don't have to maintain it in 2 separate locations, but people still can see where to find the info regarding who is an approver vs maintainer for what repo