This endpoint aggregates all checks related to <service id> on the agent
and return an appropriate http code + the string describing the worst
check.
This allows to cleanly expose service status to other component, hiding
complexity of multiple checks.
This is especially useful to use consul to feed a load balancer which
would delegate health checking to consul agent.
Exposing this endpoint on the agent is necessary to avoid a hit on
consul servers and avoid decreasing resiliency (this endpoint will work
even if there is no consul leader in the cluster).
* Adds client-side retry for no leader errors.
This paves over the case where the client was connected to the leader
when it loses leadership.
* Adds a configurable server RPC drain time and a fail-fast path for RPCs.
When a server leaves it gets removed from the Raft configuration, so it will
never know who the new leader server ends up being. Without this we'd be
doomed to wait out the RPC hold timeout and then fail. This makes things fail
a little quicker while a sever is draining, and since we added a client retry
AND since the server doing this has already shut down and left the Serf LAN,
clients should retry against some other server.
* Makes the RPC hold timeout configurable.
* Reorders struct members.
* Sets the RPC hold timeout default for test servers.
* Bumps the leave drain time up to 5 seconds.
* Robustifies retries with a simpler client-side RPC hold.
* Reverts untended delete.
* Added rate limiting for agent RPC calls.
* Initializes the rate limiter based on the config.
* Adds the rate limiter into the snapshot RPC path.
* Adds unit tests for the RPC rate limiter.
* Groups the RPC limit parameters under "limits" in the config.
* Adds some documentation about the RPC limiter.
* Sends a 429 response when the rate limiter kicks in.
* Adds docs for new telemetry.
* Makes snapshot telemetry look like RPC telemetry and cleans up comments.
