Add the most basic interfaces to OSS (#13561)

Author: sgmiller

vault/managed_key.go

@@ -0,0 +1,11 @@
+package vault
+
+import "context"
+
+type ManagedKey interface {
+	Name() string
+}
+
+type ManagedKeySystemView interface {
+	GetManagedKey(context.Context, string) (ManagedKey, error)
+}