feat(gossip-support) update gossip topology

[EclesioMeloJunior]

Description

When handling active leaves, Gossip Support checks if the session changes, in such case we should update the topology given that a new session means new authorities. To create the new gossip topology we need:

• a list of authorities (expressed as Vec<AuthorityDiscoveryId>), that is retrieved from the session info
• the randomness, retrieved from the current BABE epoch
• use fisher_yates shuffle function to shuffle these list of authorities
• Send the message NetworkBridgeRxMessage::NewGossipTopology to the overseer with the shuffled authorities

Links

https://github.com/paritytech/polkadot-sdk/blob/b30aa3193048d6bbdf21408bd0cc4503010fe3f8/polkadot/node/network/gossip-support/src/lib.rs#L674

Acceptance Criteria

• 60% of code tested