Pools: Add ability to configure commission claiming permissions (#2474)

Addresses #409.

This request has been raised by multiple community members - the ability
for the nomination pool root role to configure permissionless commission
claiming:

> Would it be possible to have a claim_commission_other extrinsic for
claiming commission of nomination pools permissionless?

This PR does not quite introduce this additional call, but amends
`do_claim_commission` to check a new `claim_permission` field in the
`Commission` struct, configured by an enum:

```
enum CommissionClaimPermission {
   Permissionless,
   Account(AccountId),
}
```
This can be optionally set in a bonded pool's
`commission.claim_permission` field:

```
struct BondedPool {
   commission: {
      <snip>
      claim_permission: Option<CommissionClaimPermission<T::AccountId>>,
   },
   <snip>
}
```

This is a new field and requires a migration to add it to existing
pools. This will be `None` on pool creation, falling back to the `root`
role having sole access to claim commission if it is not set; this is
the behaviour as it is today. Once set, the field _can_ be set to `None`
again.

#### Changes
- [x] Add `commision.claim_permission` field.
- [x] Add `can_claim_commission` and amend `do_claim_commission`.
- [x] Add `set_commission_claim_permission` call.
- [x] Test to cover new configs and call.
- [x] Add and amend benchmarks.
- [x] Generate new weights + slot into call
`set_commission_claim_permission`.
- [x] Add migration to introduce `commission.claim_permission`, bump
storage version.
- [x] Update Westend weights.
- [x] Migration working.

---------

Co-authored-by: command-bot <>