rpc-v2/tx: Rename transaction to transactionWatch (#3040)

This PR backports the changes from
https://github.com/paritytech/json-rpc-interface-spec/pull/107.

The `transaction` class becomes `transactionWatch`, and the other
functionality remains the same.

// cc @paritytech/subxt-team

---------

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

prdoc/pr_3040.prdoc

@@ -0,0 +1,14 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Rename transaction to transactionWatch
+
+doc:
+  - audience: Node Dev
+    description: |
+      Renamed `transaction_unstable_submitAndWatch` to `transactionWatch_unstable_submitAndWatch`,
+      `transaction_unstable_watchEvent` to `transactionWatch_unstable_watchEvent` and
+      `transaction_unstable_unwatch` to `transactionWatch_unstable_unwatch`.
+
+crates: 
+- name: sc-rpc-spec-v2

substrate/client/rpc-spec-v2/src/transaction/api.rs

@@ -29,8 +29,8 @@ pub trait TransactionApi<Hash: Clone> {
 	/// See [`TransactionEvent`](crate::transaction::event::TransactionEvent) for details on
 	/// transaction life cycle.
 	#[subscription(
-		name = "transaction_unstable_submitAndWatch" => "transaction_unstable_watchEvent",
-		unsubscribe = "transaction_unstable_unwatch",
+		name = "transactionWatch_unstable_submitAndWatch" => "transactionWatch_unstable_watchEvent",
+		unsubscribe = "transactionWatch_unstable_unwatch",
 		item = TransactionEvent<Hash>,
 	)]
 	fn submit_and_watch(&self, bytes: Bytes);