establish_channel_with_system (#3721)

Implements https://github.com/polkadot-fellows/RFCs/issues/82
Allow any parachain to have bidirectional channel with any system
parachains

Looking for initial feedbacks before continue finish it

TODOs:
- [x] docs
- [x] benchmarks
- [x] tests

---------

Co-authored-by: joe petrowski <25483142+joepetrowski@users.noreply.github.com>
Co-authored-by: Adrian Catangiu <adrian@parity.io>

polkadot/runtime/parachains/src/mock.rs

@@ -248,6 +248,7 @@ impl crate::dmp::Config for Test {}
 
 parameter_types! {
 	pub const FirstMessageFactorPercent: u64 = 100;
+	pub const DefaultChannelSizeAndCapacityWithSystem: (u32, u32) = (4, 1);
 }
 
 impl crate::hrmp::Config for Test {
@@ -255,6 +256,7 @@ impl crate::hrmp::Config for Test {
 	type RuntimeEvent = RuntimeEvent;
 	type ChannelManager = frame_system::EnsureRoot<u64>;
 	type Currency = pallet_balances::Pallet<Test>;
+	type DefaultChannelSizeAndCapacityWithSystem = DefaultChannelSizeAndCapacityWithSystem;
 	type WeightInfo = crate::hrmp::TestWeightInfo;
 }