txWatch: Stabilize txWatch to version 1 (#4171)
This PR stabilizes the txBroadcast API to version 1. Needs from spec: - https://github.com/paritytech/json-rpc-interface-spec/pull/153 - https://github.com/paritytech/json-rpc-interface-spec/pull/154 cc @paritytech/subxt-team --------- Signed-off-by: Alexandru Vasile <[email protected]>