Handle the `poolId` along with `party_id` in Core/Aggregator/Signer

[jpraynaud]

Need

In order to use correctly the stake distribution retrieved from the Cardano node, we need to handle properly and match:

• The poolId: unique identifier of the SPO in the stake distribution
• The party_id: unique identifier used in the Mithril protocol

Solution

• The party_id in the Mithril nodes will store the poolId from the Cardano node
• The party_id will be removed from the mithril-core library

Tasks

• Remove the party_id in mithril-core interface (and recompute it inside the lib with custom sort based on stake and verification_key) (Done in Removing PartyID from mithril-core #279)
• Switch the party_id: u64 with party_id: String in open-api.yaml
• Switch the party_id: u64 with party_id: String in mithril-common
• Switch the party_id: u64 with party_id: String in mithril-aggregator
• Switch the party_id: u64 with party_id: String in mithril-signer
• Switch the party_id: u64 with party_id: String in protocol-demo
• Reset (if needed) associated data stores on GCP