Adding Support for Multi-Party Computation Wallet with Custom Signer and Bridge

[shottah]

Hey @celo-org/applications
I want to reach out today about an issue my team is having regarding a feature enhancement to our own Valora fork.

We have replaced the @celo/wallet-base with a wallet bridge developed by Capsule Labs which implements Multi-Party Computation using a custom signer.
When it comes to signing transactions, there is a proofOfPossession that expects to sign a transaction with geth or some LocalSigner implementation.
https://github.com/celo-org/celo-monorepo/blob/339b3e3803f353662db4e5445cd2bf37375ed8e8/packages/sdk/contractkit/src/wrappers/Accounts.ts#LL335C9-L335C37
In order for us to add full support of a MPC wallet (i.e. custom wallet bridge, and signer) how should we go about this?