notify readiness when registered plugins are ready

Signed-off-by: Henry Wang <henwang@amazon.com>

Author: henry118

context.go

@@ -28,12 +28,13 @@ import (
 
 // InitContext is used for plugin initialization
 type InitContext struct {
-	Context      context.Context
-	Root         string
-	State        string
-	Config       interface{}
-	Address      string
-	TTRPCAddress string
+	Context           context.Context
+	Root              string
+	State             string
+	Config            interface{}
+	Address           string
+	TTRPCAddress      string
+	RegisterReadiness func() func()
 
 	// deprecated: will be removed in 2.0, use plugin.EventType
 	Events *exchange.Exchange