message: rpc: fix RPC help requirements for getblocktemplate
  First argument is optional, and defaults to {mode:template}.
diff: @@ -302,7 +302,7 @@ static UniValue getblocktemplate(const JSONRPCRequest& request)
  " https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki#getblocktemplate_changes\n"
  " https://github.com/bitcoin/bips/blob/master/bip-0145.mediawiki\n",
  {
  - {"template_request", RPCArg::Type::OBJ, RPCArg::Optional::NO, "A json object in the following spec",
  + {"template_request", RPCArg::Type::OBJ, "{}", "A json object in the following spec",
  {
  {"mode", RPCArg::Type::STR, /* treat as named arg */ RPCArg::Optional::OMITTED_NAMED_ARG, "This must be set to \"template\", \"proposal\" (see BIP 23), or omitted"},
  {"capabilities", RPCArg::Type::ARR, /* treat as named arg */ RPCArg::Optional::OMITTED_NAMED_ARG, "A list of strings",
  