Add chain/addTransaction for signed transaction

[hairtail]

Summary

Add chain/postTransaction to post/broadcast an already signed transaction.

Testing Plan

Documentation

Does this change require any updates to the Iron Fish Docs (ex. the RPC API
Reference)? If yes, link a
related documentation pull request for the website.

Yes

Breaking Change

Is this a breaking change? If yes, add notes below on why this is breaking and
what additional work is required, if any.

[ ] Yes

[hairtail]

Guess i should tell the reason why this PR and this rpc route again. As i have said days before #3666, in my opinion and as most projects did (like btc, ethereum, filecoin etc), the chain based routes (like getBlock getNoteWitness) should be public accessible while the wallet based routes (like create sendTransaction) should be strictly limited.

[hughy]

acceptTransaction could return false if the mempool already has the transaction. Should this endpoint continue even if acceptTransaction returns false in that case?

[hairtail]

'Mempool reject' or 'Add transaction fails' should be returned in my opinion.

[holahula]

Hi @hairtail, this functionality will be added in #3742. Am I good to close this PR?

There are a few changes to functionality:

• The endpoint will always broadcast as long as the transaction is validated. This is useful for re-broadcasting.
• Being accepted into the mempool should not stop broadcasting because there are additional criteria for being accepted into the mempool that should not affect this functionality.

[hairtail]

Functionality will be added in another PR by the team.