Add XCM pallet and config to Polkadot runtime (#4313)

* xcm added

* xcm pallet & config added Polkadot

* set advertise XCM version to 2 for Polkadot

* remove ChildSystemParachainAsSuperuser from Polkadot XCM config

* remove unpaid execution for system parachains

* remove unused imports

Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

polkadot/Cargo.lock

@@ -6772,6 +6772,7 @@ dependencies = [
  "pallet-treasury",
  "pallet-utility",
  "pallet-vesting",
+ "pallet-xcm",
  "parity-scale-codec",
  "polkadot-primitives",
  "polkadot-runtime-common",
@@ -6804,6 +6805,9 @@ dependencies = [
  "substrate-wasm-builder",
  "tiny-keccak",
  "trie-db",
+ "xcm",
+ "xcm-builder",
+ "xcm-executor",
 ]
 
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