Full multisig group state sync for new member

[kentbull]

Feature request description/rationale

Request Rationale

Currently when a prospective participant joins a multisig group then all of the state of the current multisig group is not replicated to the new participant's LMDB database. This prevents the new member from using any registries or credentials the multisig group has created. The lack of registry replication has been known for some time.

Some community members, including Nord vLEI, have hit this issue and it prevents effective scaling of their multisig groups after those groups have created registries or issued credentials. See keria issue #316 (Joined member of multisig can't access registries) for some details and the linked issue KERIA #283 (Feature request: a way for a multisig member to catch up updates).

Specific Request

The feature request is the following:
On joining a multisig group a participant, whether single sig or multisig, should receive the following from the multisig group members:

1. All key event logs (similar to what kli local watch and kli multisig update currently do)
2. All credential registries.
3. All ACDC credentials
4. All signatures, attachments, indexes, or any other cryptographic material used for the multisig group that would be considered part of the multisig group identifier state.