Bootstrap Certificate Chain w/ Genesis Certificate

[jpraynaud]

Issue

Create a genesis command of the Aggregator (manual operation):

• (Re)Use a private key (Cardano keys) for testing purpose
• (Re)Use a public key stored on a public location (Github)
• Create and store a Genesis Certificate that embeds the AVK of the Stake Distribution and its Genesis Signature in the Aggregator
• Verify the Genesis Certificate in the Client
• Implement this feature in the End to End Tests

Tasks

• [x] Add a Genesis Signer that signs a message with a Genesis Secret Key (only for test purpose)
• [x] Add a Genesis Verifier that verifies a Genesis Signature against a Genesis Verification Key
• [x] Implement the verify_genesis_certificate of the Certificate Verifier
• [x] Make Client load/use the Genesis Verification Key
• [x] Make Aggregator load/use the Genesis Verification Key
• [x] Make Aggregator verify that the Certificate Chain is valid before trying to produce new Mithril Certificates
• [x] Add a sub command to the Aggregator CLI to generate test only Genesis Keys, and boostrap a test only Genesis Certificate
• [x] Add a sub command to the Aggregator CLI to export the message that must be signed with Genesis Secret Key into a Genesis Signature
• [x] Add a sub command to the Aggregator CLI to import the Genesis Signature and create a Genesis Certificate
• [x] Update test lab to bootstrap a Genesis Certificate
• [x] Update devnet standalone to bootstrap a Genesis Certificate
• [x] Update GCP Aggregator to use the test Genesis Keys
• [ ] Fix flakiness test end to end in CI
• [ ] Update documentations
• [ ] Deploy to GCP Aggregator (and bootstrap Genesis Certificate)

Depends on #316