Put HRMP Channel Management on General Admin Track (#7477)

* create ManagerOrigin for HRMP

* missed one

* fix mock

* update GeneralAdmin docs

polkadot/runtime/test-runtime/src/lib.rs

@@ -543,6 +543,7 @@ parameter_types! {
 impl parachains_hrmp::Config for Runtime {
 	type RuntimeOrigin = RuntimeOrigin;
 	type RuntimeEvent = RuntimeEvent;
+	type ChannelManager = frame_system::EnsureRoot<AccountId>;
 	type Currency = Balances;
 	type WeightInfo = parachains_hrmp::TestWeightInfo;
 }