Partially resolves #1521

Summary

This PR updates the collator selection mechanism to governance approved system. A candidate applicant needs to apply first by reserving the bond and only once application is approved by governanace the node is added to collator candidates. Also governanace can kick & slash bad performing collator candidates.

The pallet uses two configurable origins for governance actions

• GovernanceOrigin: Can approve/close candidacy applications
• ForceRemovalOrigin: Can forcibly kick and slash candidates

The following extrinsincs are added,

• apply_for_candidacy: Apply to be a candidate by reserving bond
• close_application: Close pending candidate application, unreserve the bond.
• approve_application: Approve the candidate application, add node to candidates. (Only GovernanceOrigin)
• kick_candidate: Kick and slash a candidate immediately. (Only ForceRemovalOrigin)
  • If governance wish to remove a candidate without slashing, it can be done via wrapping the leave_intent call with utility's dispatch_as via a referendum

Note:-

The old register_as_candidate is deprecated and will fail with Permission error (should be removed?)

Configs

For Astar & Shibuya

• GovernanceOrigin: 2/3 MainCouncil OR Referendum
• ForceRemovalOrigin: 2/3 MainCouncil OR Referendum

For Shiden, both root account

TODO

• Finalise the origins config for Astar
• Astar Docs PR

Check list**

• added or updated unit tests
• updated Astar official documentation
• added benchmarks & weights for any modified runtime logics.