Research and Design Grandpa Catch-Up

## Issue summary

To utilize the neighbor message protocol to receive commit messages we first need to catch up to the current voter set and round. This is done via the grandpa catch-up process. This issue is to research and design an MVP catch-up protocol to enable us to catch up to the current grandpa state.

The completion criteria for this issue are:
- Design the catch-up protocol
- Create all issues highlighting the implementation of the design

## Other information and links

- https://spec.polkadot.network/chap-networking#sect-grandpa-catchup-messages
- https://spec.polkadot.network/sect-finality#sect-grandpa-catchup

Start with the linked Polkadot specifications for GRANDPA catch-up messages and the GRANDPA catch-up process. Define the MVP protocol needed to reach the current voter set and round, then record separate implementation issues for each part. Done means the protocol design is documented and all implementation tasks have been created.

Written by the indexing model from the issue text.