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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result_inner.pushKV("allowed", true);
                        result_inner.pushKV("vsize", virtual_size);
                        UniValue fees(UniValue::VOBJ);
                        fees.pushKV("base", ValueFromAmount(fee));
                        fees.pushKV("effective-feerate", ValueFromAmount(tx_result.m_effective_feerate.value().GetFeePerK()));
                        UniValue effective_includes_res(UniValue::VARR);
                        for (const auto& wtxid : tx_result.m_wtxids_fee_calculations.value()) {
                            effective_includes_res.push_back(wtxid.ToString());
                        }
                        fees.pushKV("effective-includes", effective_includes_res);
                        result_inner.pushKV("fees", fees);
                    }
                } else {
                    result_inner.pushKV("allowed", false);
                    const TxValidationState state = tx_result.m_state;
                    if (state.GetResult() == TxValidationResult::TX_MISSING_INPUTS) {
                        result_inner.pushKV("reject-reason", "missing-inputs");
                    } else {
                        result_inner.pushKV("reject-reason", state.GetRejectReason());
                    }
                }
                rpc_result.push_back(result_inner);
            }
            return rpc_result;
        },
    };
}
static std::vector<RPCResult> MempoolEntryDescription()