message: doc: Mark proprietary array optional
  Also, remove not needed '\n's.
  Can be reviewed with --word-diff-regex=.
diff: @@ -1040,8 +1040,9 @@ static RPCHelpMan testmempoolaccept()
  static RPCHelpMan decodepsbt()
  {
  - return RPCHelpMan{"decodepsbt",
  - "\nReturn a JSON object representing the serialized, base64-encoded partially signed Peercoin transaction.\n",
  + return RPCHelpMan{
  + "decodepsbt",
  + "Return a JSON object representing the serialized, base64-encoded partially signed Peercoin transaction.",
  {
  {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "The PSBT base64 string"},
  },
  @@ -1150,7 +1151,7 @@ static RPCHelpMan decodepsbt()
  {
  {RPCResult::Type::STR_HEX, "key", "(key-value pair) An unknown key-value pair"},
  }},
  - {RPCResult::Type::ARR, "proprietary", "The input proprietary map",
  + {RPCResult::Type::ARR, "proprietary", /*optional=*/true, "The input proprietary map",
  {
  {RPCResult::Type::OBJ, "", "",
  {
  @@ -1191,7 +1192,7 @@ static RPCHelpMan decodepsbt()
  {
  {RPCResult::Type::STR_HEX, "key", "(key-value pair) An unknown key-value pair"},
  }},
  - {RPCResult::Type::ARR, "proprietary", "The output proprietary map",
  + {RPCResult::Type::ARR, "proprietary", /*optional=*/true, "The output proprietary map",
  {
  {RPCResult::Type::OBJ, "", "",
  {
  