[Bug] Multisig v2 does not check for well-formed transactio

[wnhedaxx]

🐛 Bug Report

When submitting a single-signer transaction, the CLI/REST client check that a transaction is well formed, e.g. that the public entry function call corresponds to an existing function and has proper arguments/type arguments

However, when submitting a transaction proposal for multisig v2, there is no such well-formed check, rather, the multisig v2 appears to simply accept for the transaction payload an arbitrary bytestring, e.g. a function call with any combination of type args/args

This can create headaches during the multisig flow, where transactions need to be rejected after faulty submission, even though the underlying proposed transaction could've been rejected upon proposal, since it was not well-formed

(This does not apply for creating a txn proposal with payload hash only)

[wnhedaxx]

@d0cd