These endpoints are similar to the `sendrawtransaction` RPC, with some differences:
1. They take a serialized `BroadcastTx(s)Request` (similar to most Chronik endpoints)
2. They perform an SLP/ALP check and reject all txs atomically if any tokens are unintentionally burned
Currently /broadcast-txs, after the token check, simply broadcasts txs one by one and not as a package. This matches the current NNG Chronik behavior, but in the future we could use the SubmitPackage function from the node to make that atomic, too.
Depends on D15369.