While some protocols require value attached to OP_RETURN outputs, this otherwise seems like a mistake.

Setting the value to 0 should really be done by the wallet/script creating the transaction (like createrawtransaction does for `data` outputs). However, as an additional check, similar to the high-fee check, sendrawtransaction could also check for non-zero value OP_RETURN outputs.

This should be configurable by a new RPC argument.

See also https://transactionfee.info/charts/output-opreturn-amount/

#### Useful skills:

* Bitcoin Core RPC code
* Transaction output types
* Bitcoin Core functional tests

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}},
                    }}
                }},
                {RPCResult::Type::ARR, "replaced-transactions", true, "List of txids of replaced transactions",
                {
                    {RPCResult::Type::STR_HEX, "", "The transaction id"},
                }},
            },
        },
        RPCExamples{
            HelpExampleCli("testmempoolaccept", "[rawtx1, rawtx2]") +
            HelpExampleCli("submitpackage", "[rawtx1, rawtx2]")
        },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
        {
            if (!Params().IsMockableChain()) {
                throw std::runtime_error("submitpackage is for regression testing (-regtest mode) only");
            }
            const UniValue raw_transactions = request.params[0].get_array();
            if (raw_transactions.size() < 1 || raw_transactions.size() > MAX_PACKAGE_COUNT) {
                throw JSONRPCError(RPC_INVALID_PARAMETER,
                                   "Array must contain between 1 and " + ToString(MAX_PACKAGE_COUNT) + " transactions.");
            }
            std::vector<CTransactionRef> txns;
            txns.reserve(raw_transactions.size());
            for (const auto& rawtx : raw_transactions.getValues()) {
                CMutableTransaction mtx;
                if (!DecodeHexTx(mtx, rawtx.get_str())) {
                    throw JSONRPCError(RPC_DESERIALIZATION_ERROR,
                                       "TX decode failed: " + rawtx.get_str() + " Make sure the tx has at least one input.");