Use custom type for ProtocolName (#12172)

* Add ProtocolName custom type

* Use new ProtocolName in sc_network_common

* Use new ProtocolName in sc_network

* Use new ProtocolName for BEEFY and GRANDPA

* Use new ProtocolName for notifications

* Use new ProtocolName in sc_network (part 2)

* Use new ProtocolName in sc_network_gossip

* Use new ProtocolName in sc_offchain

* Remove unused imports

* Some more fixes

* Add tests

* Fix minor import issues

* Re-export ProtocolName in sc_network

* Revert "Re-export ProtocolName in sc_network"

This reverts commit 8d8ff71927e7750757f29c9bbd88dc0ba181d214.

* Re-export ProtocolName in sc_network

* Remove dependency on sc-network-common from beefy-gadget