sc-network: expose `add_to_priority_group` and `remove_from_priority_… (#7247)

* sc-network: expose `add_to_priority_group` and `remove_from_priority_group` in `NetworkService`

* sc-network: fix a typo

* Update client/network/src/service.rs

Co-authored-by: Max Inden <[email protected]>

* s/parse_multiaddr/split_multiaddr_and_peer_id/g

* sc-network: mark new functions as async and add comments

* Apply suggestions from code review

Co-authored-by: Max Inden <[email protected]>

Co-authored-by: Max Inden <[email protected]>