feat(controller): Add health endpoint (#1882)

* feat(controller): New health service and server

This change also implements a new listener purpose, `ops`.

`ops` (short for operations) is a new listener purpose that is
responsible for serving Boundary's operations endpoints, like health
and possibly metrics.

At Startup: `ops` listeners get configured as late as possible to catch
any errors with the startup process;

At Shutdown: If the health endpoint has been set-up, we introduce a
configurable delay in the process. This is to enable the health endpoint
to report unhealthy for that amount of time. `ops` listeners are also
the last listeners to be shutdown.

internal/servers/controller/testing.go

@@ -576,7 +576,7 @@ func TestControllerConfig(t *testing.T, ctx context.Context, tc *TestController,
 	for _, listener := range opts.Config.Listeners {
 		listener.RandomPort = true
 	}
-	if err := tc.b.SetupListeners(nil, opts.Config.SharedConfig, []string{"api", "cluster"}); err != nil {
+	if err := tc.b.SetupListeners(nil, opts.Config.SharedConfig, []string{"api", "cluster", "ops"}); err != nil {
 		t.Fatal(err)
 	}
 	if err := tc.b.SetupControllerPublicClusterAddress(opts.Config, ""); err != nil {