Staking festival end storage cleanup

[Dinonard]

Pull Request Summary

Support for clearing old storage items from Astar once we end the staking festival. Solution has been tested on local network and works fine.

Upgrade Flow

1. Using sudo, unregister all contracts
2. Use binary built with try-runtime features to simulate runtime upgrade logic on Astar and confirm it works
3. Initiate runtime upgrade for Astar network with latest dapps-staking
4. Once new runtime is applied, pallet will enter maintenance mode
5. We will need to call do_upgrade call a few times in order to cleanup old storage items
6. Once last item is cleared, maintenance mode will be disabled an pallet will resume normal operation
7. :tada: :tada: :tada: we've re-launched!

TODO

• [x] beef up era 1 reward
• [x] decide unbonding period for Astar

Check list

• [ ] contains breaking changes
• [x] adds new feature
• [x] modifies existing feature (bug fix or improvements)
• [ ] relies on other tasks
• [ ] documentation changes
• [x] tests and/or benchmarks are included
• [ ] changed API client type definition or chain metadata