Once a peering is marked for deletion a new leader routine will now
clean up all imported resources and then the peering itself.
A lot of the logic was grabbed from the namespace/partitions deferred
deletions but with a handful of simplifications:
- The rate limiting is not configurable.
- Deleting imported nodes/services/checks is done by deleting nodes with
the Txn API. The services and checks are deleted as a side-effect.
- There is no "round rate limiter" like with namespaces and partitions.
This is because peerings are purely local, and deleting a peering in
the datacenter does not depend on deleting data from other DCs like
with WAN-federated namespaces. All rate limiting is handled by the
Raft rate limiter.
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)