[Feature] Limit collectives teleports to DOT (#1579)

* [Feature] Limit collectives teleports to DOT

* Update pallets/xcm/src/lib.rs

Co-authored-by: Keith Yeung <[email protected]>

* fix review comments

* Update parachains/runtimes/collectives/collectives-polkadot/src/xcm_config.rs

Co-authored-by: Chevdor <[email protected]>

* [ci] Apply cargo-fmt

Co-authored-by: Keith Yeung <[email protected]>
Co-authored-by: Chevdor <[email protected]>
Co-authored-by: paritytech-ci <[email protected]>