Simplify trait bounds in network to prepare for collator-rpc (#12082)

* Hack towards PoC

* Abstract away runtime requirement

* blockchainevents

* Remove bitswap

* Remove unused sync more

* Remove unused features in network

* Re-enable bitswap change

* Remove `Chain` trait bound

* Reimplement blockchain-rpc-events

* Move network to cumulus

* Make AuthorityDiscovery async

* Remove `ProofProvider` requirement from network behaviour

* Extract bitswap

* Adjustments after merge

* Remove HeaderMetadata trait from network

* Introduce NetworkHeaderBackend

* Add comments

* Improve comments

* Move NetworkHeaderBackend to new module

* Improve naming, remove redundand send + sync

* Clean up generics

* Fix CI

* Improve comment and readability

* Remove NetworkHeaderBackend

* Fix Cargo.lock

Co-authored-by: Sebastian Kunert <skunert@Sebastians-MacBook-Pro.fritz.box>