Multiple aggregators on a Mithril Network PoC

[jpraynaud]

Why

We want to allow multiple aggregators to run on the same Mithril network. Before going through a fully decentralized implementation, we want to implement a prototype version of the Centralized signer registration and broadcast architecture.

What

• The Mithril aggregator can run either in the master or the slave role in a Mithril network depending on configuration parameters.
• The master aggregator is registered in the slave aggregators.
• The slave aggregator synchronize its signer registrations with the master aggregator at epoch transition (and feed its store with the next signers registration information)
• The slave aggregator never accepts signer registration on its REST API
• The slave aggregators is able to produce its own independent certificate chain and artifacts for the Mithril data types (in devnet and testnets only).
• The Mithril clients can interact seamlessly with any of the aggregators to download and verify Cardano database, transactions or stake distribution snapshots.
• The certificate chain and protocol parameters synchronization will be implemented in a future issue

How

• Implement a slave mode for the signer registration in the aggregator #2334
• Add integration test for mode for the signer registration in the aggregator #2335
• Adapt the e2e test to support multiple aggregators (with p2p mode only)
• Adapt the infra to support multiple aggregators?