Staking: Add deprecate_controller_batch AdminOrigin call (#2589)

Partially Addresses #2500

Adds a `deprecate_controller_batch` call to the staking pallet that is
callable by `Root` and `StakingAdmin`. To be used for controller account
deprecation and removed thereafter. Adds
`MaxControllersDeprecationBatch` pallet constant that defines max
possible deprecations per call.

- [x] Add `deprecate_controller_batch` call, and
`MaxControllersInDeprecationBatch` constant.
- [x] Add tests, benchmark, weights. Tests that weight is only consumed
if unique pair.
- [x] Adds `StakingAdmin` origin to staking's `AdminOrigin` type in
westend runtime.
- [x] Determined that worst case 5,900 deprecations does fit into
`maxBlock` `proofSize` and `refTime` in both normal and operational
thresholds, meaning we can deprecate all controllers for each network in
one call.

## Block Weights

By querying `consts.system.blockWeights` we can see that the
`deprecate_controller_batch` weights fit within the `normal` threshold
on Polkadot.

#### `controller_deprecation_batch` where i = 5900:
#### Ref time: 69,933,325,300
#### Proof size: 21,040,390

### Polkadot 

```
// consts.query.blockWeights

maxBlock: {
        refTime: 2,000,000,000,000
        proofSize: 18,446,744,073,709,551,615
}
normal: {
 maxExtrinsic: {
	refTime: 1,479,873,955,000
	proofSize: 13,650,590,614,545,068,195
 }
 maxTotal: {
	refTime: 1,500,000,000,000
	proofSize: 13,835,058,055,282,163,711
 }
}
```

### Kusama

```
// consts.query.blockWeights

  maxBlock: {
    refTime: 2,000,000,000,000
    proofSize: 18,446,744,073,709,551,615
  }
    normal: {
      maxExtrinsic: {
        refTime: 1,479,875,294,000
        proofSize: 13,650,590,614,545,068,195
      }
      maxTotal: {
        refTime: 1,500,000,000,000
        proofSize: 13,835,058,055,282,163,711
      }
}
```

---------

Co-authored-by: command-bot <>
Co-authored-by: Gonçalo Pestana <g6pestana@gmail.com>

substrate/frame/staking/src/mock.rs

@@ -122,6 +122,7 @@ parameter_types! {
 	pub static SlashDeferDuration: EraIndex = 0;
 	pub static Period: BlockNumber = 5;
 	pub static Offset: BlockNumber = 0;
+	pub static MaxControllersInDeprecationBatch: u32 = 5900;
 }
 
 #[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
@@ -316,6 +317,7 @@ impl crate::pallet::pallet::Config for Test {
 	type NominationsQuota = WeightedNominationsQuota<16>;
 	type MaxUnlockingChunks = MaxUnlockingChunks;
 	type HistoryDepth = HistoryDepth;
+	type MaxControllersInDeprecationBatch = MaxControllersInDeprecationBatch;
 	type EventListeners = EventListenerMock;
 	type BenchmarkingConfig = TestBenchmarkingConfig;
 	type WeightInfo = ();