Payees lazy migration to PayoutDestination, Split variant for payouts, remove Controller

[rossbulat]

Tracking issue: #1195

This PR is part 1 of a lazy migration to update reward destinations, which removes Controller, refactors RewardDestination into a new PayoutDestination enum, and adds an additional Split enum for the ability to compound a part of rewards and have the rest as free balance.

• Create PayoutDestination with new variants and introduce Payees storage item to replace Payee.
• set_payee removes Payee (RewardDestination) and inserts to Payees (PayoutDestination)
• Introduce update_payee call to lazily migrate from Payee to Payees storage item.
• Implement Split logic on payout_stakers with getter that migrates Payee to new Payees storage.
• Review staking benchmarks and ensure they are worst case scenario (Split, existing Payee).
• Add tests again for fee-less update_payee.
• Add tests for get_payout_destination, ensure Payees is populated.

[paritytech-cicd-pr]

The CI pipeline was cancelled due to failure one of the required jobs.
Job name: test-linux-stable 1/3
Logs: https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/3959041

[rossbulat]

Just a note for AppSec, this PR has broken due to a ledger refactor & needs to be fixed. It'll involve rebuilding the PR from the latest master I imagine. I will take a stab this week.

[bkchr]

@Ank4n why was this never merged? Should we now close this pr?

[Ank4n]

@Ank4n why was this never merged? Should we now close this pr?

This is probably blocked by #3706 that is not yet executed.
@rossbulat @gpestana Is this PR still valid?

[rossbulat]

There was a lack of interest in reviewing and finalising this so it never got past the finish line.

It can be closed and reimplemented as the codebase has changed and I don't have org access to manage this PR anymore.