transaction-pool: drop unpropagable txs if local node cant author blocks (#8048)

* transaction-pool: drop unpropagable txs if local node cant author blocks

* fix test compilation

* transaction-pool: remove unnecessary static bound on CanAuthor

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* rpc-api: add translation for PoolError::Unactionable

* transaction-pool: add test for rejecting unactionable transactions

* basic-authorship: fix doc test

* transaction-pool: fix benchmark compilation

* transaction-pool: rename CanAuthor to IsValidator

* transaction-pool: nit in error message

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

substrate/primitives/transaction-pool/src/error.rs

@@ -60,6 +60,9 @@ pub enum Error {
 	#[error("Transaction couldn't enter the pool because of the limit")]
 	ImmediatelyDropped,
 
+	#[error("Transaction cannot be propagated and the local node does not author blocks")]
+	Unactionable,
+
 	#[from(ignore)]
 	#[error("{0}")]
 	InvalidBlockId(String),