Add Invocation Resource Mode

diff --git a/plan.go b/plan.go
index 6158684..a987d17 100644
--- a/plan.go
+++ b/plan.go

@@ -26,6 +26,9 @@
 
 	// ManagedResourceMode is the resource mode for managed resources.
 	ManagedResourceMode ResourceMode = "managed"
+
+	// For Actions
+	ActionInvocationResourceMode ResourceMode = "action"
 )
 
 // Plan represents the entire contents of an output Terraform plan.