babe: treat epoch_authorship RPC method as unsafe (#6069)

* service: pass DenyUnsafe to rpc extensions

* node: add DenyUnsafe to rpc full node dependencies

* client: fix whitespace in rpc policy file

* babe: treat epochAuthorship rpc method as unsafe

* babe: add test for unsafe rpc method

* babe: rename babe rpc handler

* service: traitify rpc extension builder

* service: make the rpc extensions builder api non-breaking

* service: revert changes from light node rpc extensions builder

* node: remove unnecessary type in service creation

* service: cleanup with_rpc_extensions implementation

* service: add missing docs to RpcExtensionBuilder