Decide relaying strategy

[gjermundgaraba]

For counterparty chain relaying, we need to use the sidecar for relaying, but for the attestation chain we could potentially enshrine the relaying as part of the vote extension process.

Pros for enshrined relaying:

• No need for fees
• Faster (same block as update client)

Cons for enshrined relaying

• Need to implement, monitor two separate relaying strategies (since we need it for the counterparty chain in any case)
• Potentially some performance issues with putting too much work into the vote extensions
  • That said, we can hopefully prepare everything in the sidecar so we won't need to do any queries in the vote extension processes