Implement Mithril Relay in infra

[jpraynaud]

Content

This PR includes an optional implementation of a Mithril Relay in the infrastructure.
Here is the list of available signer types after this modification:

• verified: verified pool ids for signers associated to SPO Cardano Block Producer and Cardano Relay nodes, and uses a Mithril Relay
• verified-norelay: verified pool ids for signers associated to SPO Cardano Block Producer and Cardano Relay nodes, and without a Mithril Relay
• unverified: declarative pool ids for signers associated to a non SPO Cardano full node and uses a Mithril Relay (legacy)
• unverified-norelay: declarative pool ids for signers associated to a non SPO Cardano full node and without a Mithril Relay (legacy)
• unverified-alone: declarative pool ids for signers which uses the aggregator Cardano node database folder without a Mithril Relay (legacy)

Pre-submit checklist

• Branch
  • Crates versions are updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • No clippy warnings in the CI
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

Issue(s)

Closes #1018