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

#### Want to work on this issue?

For guidance on contributing, please read [CONTRIBUTING.md](https://github.com/bitcoin/bitcoin/blob/master/CONTRIBUTING.md) before opening your pull request.

{
    return RPCHelpMan{"getmempoolinfo",
        "Returns details on the active state of the TX memory pool.",
        {},
        RPCResult{
            RPCResult::Type::OBJ, "", "",
            {
                {RPCResult::Type::BOOL, "loaded", "True if the mempool is fully loaded"},
                {RPCResult::Type::NUM, "size", "Current tx count"},
                {RPCResult::Type::NUM, "bytes", "Sum of all virtual transaction sizes as defined in BIP 141. Differs from actual serialized size because witness data is discounted"},
                {RPCResult::Type::NUM, "usage", "Total memory usage for the mempool"},
                {RPCResult::Type::STR_AMOUNT, "total_fee", "Total fees for the mempool in " + CURRENCY_UNIT + ", ignoring modified fees through prioritisetransaction"},
                {RPCResult::Type::NUM, "maxmempool", "Maximum memory usage for the mempool"},
                {RPCResult::Type::STR_AMOUNT, "mempoolminfee", "Minimum fee rate in " + CURRENCY_UNIT + "/kvB for tx to be accepted. Is the maximum of minrelaytxfee and minimum mempool fee"},
                {RPCResult::Type::STR_AMOUNT, "minrelaytxfee", "Current minimum relay fee for transactions"},
                {RPCResult::Type::NUM, "incrementalrelayfee", "minimum fee rate increment for mempool limiting or replacement in " + CURRENCY_UNIT + "/kvB"},
                {RPCResult::Type::NUM, "unbroadcastcount", "Current number of transactions that haven't passed initial broadcast yet"},
                {RPCResult::Type::BOOL, "fullrbf", "True if the mempool accepts RBF without replaceability signaling inspection"},
            }},
        RPCExamples{
            HelpExampleCli("getmempoolinfo", "")
            + HelpExampleRpc("getmempoolinfo", "")
        },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    return MempoolInfoToJSON(EnsureAnyMemPool(request.context));
},
    };
}
static RPCHelpMan savemempool()