fa0815c300 rpc: Correctly name arguments (Jon Layton)
Pull request description:
Consistently use the same name to describe arguments in the documentation and add a test that uses the name.
By splitting it up, the changes are easier to potentially backport and also make review easier when we switch to `RPCHelpMan`.
The tests should pass with or without the changes in `src`.
Partly stolen from #14459 (More RPC help description fixes by ch4ot1c)
Tree-SHA512: 1072992b1e93ac41006613523e54a0a8004f529fcb101eb9d74d91474abb0945a5a7539f249905151b904b87448f9efc0cacbd9e052fbe2ea9111e62f3e7249c
Backport of Core PR14720
https://github.com/bitcoin/bitcoin/pull/14720/