[bitcoin/bitcoin] Add tests for RPC help (#14020)

MarcoFalke commented on this pull request.

> @@ -152,6 +152,7 @@
‘p2p_node_network_limited.py’,
‘feature_blocksdir.py’,
‘feature_config_args.py’,
+ ‘rpc_help.py’,
‘feature_help.py’,

Imo this could be combined into the feature_help test. Just adding a new function there `def rpc_help(self): …` and moving the other code into `def cli_help(self): …`.