Support backup relayers

[rach-id]

Summary

It would be nice to have a flag in the relayer that checks whether no official relayer has updated the contract for some period of time, and act as backup for it.

Problem Definition

The official relayer can fail, and we want to give people the ability to relaying case no one is relaying attestations for Blobstream not to halt.

Proposal

Add a flag that backup relayers, i.e. relayers not run by official entities, can use so that their relayer can submit transactions if the official ones fail.

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned