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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for (const uint256& hash : vtxid)
            a.push_back(hash.ToString());
        if (!include_mempool_sequence) {
            return a;
        } else {
            UniValue o(UniValue::VOBJ);
            o.pushKV("txids", a);
            o.pushKV("mempool_sequence", mempool_sequence);
            return o;
        }
    }
}
static RPCHelpMan getrawmempool()
{
    return RPCHelpMan{"getrawmempool",
        "\nReturns all transaction ids in memory pool as a json array of string transaction ids.\n"
        "\nHint: use getmempoolentry to fetch a specific transaction from the mempool.\n",
        {
            {"verbose", RPCArg::Type::BOOL, RPCArg::Default{false}, "True for a json object, false for array of transaction ids"},
            {"mempool_sequence", RPCArg::Type::BOOL, RPCArg::Default{false}, "If verbose=false, returns a json object with transaction list and mempool sequence number attached."},
        },
        {
            RPCResult{"for verbose = false",
                RPCResult::Type::ARR, "", "",
                {
                    {RPCResult::Type::STR_HEX, "", "The transaction id"},
                }},
            RPCResult{"for verbose = true",
                RPCResult::Type::OBJ_DYN, "", "",
                {