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/bin/node/bench/src/txpool.rs

@@ -74,6 +74,7 @@ impl core::Benchmark for PoolBenchmark {
 		let executor = sp_core::testing::TaskExecutor::new();
 		let txpool = BasicPool::new_full(
 			Default::default(),
+			true.into(),
 			None,
 			executor,
 			context.client.clone(),