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.

{ "sendtoaddress", 4, "subtractfeefromamount" },
    { "sendtoaddress", 5 , "replaceable" },
    { "sendtoaddress", 6 , "conf_target" },
    { "sendtoaddress", 8, "avoid_reuse" },
    { "sendtoaddress", 9, "fee_rate"},
    { "sendtoaddress", 10, "verbose"},
    { "settxfee", 0, "amount" },
    { "sethdseed", 0, "newkeypool" },
    { "getreceivedbyaddress", 1, "minconf" },
    { "getreceivedbyaddress", 2, "include_immature_coinbase" },
    { "getreceivedbylabel", 1, "minconf" },
    { "getreceivedbylabel", 2, "include_immature_coinbase" },
    { "listreceivedbyaddress", 0, "minconf" },
    { "listreceivedbyaddress", 1, "include_empty" },
    { "listreceivedbyaddress", 2, "include_watchonly" },
    { "listreceivedbyaddress", 4, "include_immature_coinbase" },
    { "listreceivedbylabel", 0, "minconf" },
    { "listreceivedbylabel", 1, "include_empty" },
    { "listreceivedbylabel", 2, "include_watchonly" },
    { "listreceivedbylabel", 3, "include_immature_coinbase" },
    { "getbalance", 1, "minconf" },
    { "getbalance", 2, "include_watchonly" },
    { "getbalance", 3, "avoid_reuse" },
    { "getblockfrompeer", 1, "peer_id" },
    { "getblockhash", 0, "height" },
    { "waitforblockheight", 0, "height" },
    { "waitforblockheight", 1, "timeout" },
    { "waitforblock", 1, "timeout" },
    { "waitfornewblock", 0, "timeout" },
    { "listtransactions", 1, "count" },