This PR updates the `get_channel_participant_details` method to reduce
the mixing of concerns within the method.
The authorization check for the caller has been moved to the outside,
along with the conversions from the database representations to the RPC
proto representations.
Now the method is just responsible for dealing with the data fetching,
which will make it easier to swap out.
Release Notes:
- N/A
Marshall Bowers
5894f5d2e1