Adapt infrastructure for multiple aggregators with leader/follower signer registration

[jpraynaud]

Why

We want to adapt the current infrastructure to support multiple aggregators which run with the leader/follower signer registration (only for test networks).

What

Evolve the infrastructure so that it supports running optionally multiple slave aggregators.

How

• Update the terraform infrastructure:
  • An optional leader aggregator
  • An optional bootstrap peer for the P2P network
  • Passthrough or P2P for signer registration in the signer relay
  • Passthrough or P2P for signature registration in the signer relay
  • Adapt the aggregator infrastructure
  • Adapt the signer infrastructure
  • Adapt the CI workflows
  • Add a new dev-follower-preview network