I noticed that the JSON api endpoints for peerings json encodes protobufs directly, rather than converting them into their `api` package equivalents before marshal/unmarshaling them.
I updated this and used `mog` to do the annoying part in the middle.
Other changes:
- the status enum was converted into the friendlier string form of the enum for readability with tools like `curl`
- some of the `api` library functions were slightly modified to match other similar endpoints in UX (cc: @ndhanushkodi )
- peeringRead returns `nil` if not found
- partitions are NOT inferred from the agent's partition (matching 1.11-style logic)
