fn: lb-agent: Add Runner Scheduler/Execution Stats (#1107)

LB agent reports lb placer latency. It should also report
how long it took for the runner to initiate the call as
well as execution time inside the container if the runner
has accepted (committed) to the call.

test/fn-system-tests/system_test.go

@@ -219,6 +219,7 @@ func SetUpLBNode(ctx context.Context) (*server.Server, error) {
 
 	keys := []string{"fn_appname", "fn_path"}
 	pool.RegisterPlacerViews(keys)
+	agent.RegisterLBAgentViews(keys)
 
 	// Create an LB Agent with a Call Overrider to intercept calls in GetCall(). Overrider in this example
 	// scrubs CPU/TmpFsSize and adds FN_CHEESE key/value into extensions.