staking: emit ABCI events for validator state transitions

[conorsch]

Is your feature request related to a problem? Please describe.
Currently, the most authoritative view of the active validator set is obtained by running pcli query validator list --show-inactive. We have partial, but crucially flawed, metrics related to validator states that should be removed.

Describe the solution you'd like
When a validator changes state, e.g. from Defined -> Active, or Active -> Jailed, or Active -> Tombstoned, an ABCI event should be emitted. This would allow external tooling like block explorers to consume these events.

Describe alternatives you've considered
We've tried to shore up the emitted metrics, but decided these aren't the right way to represent the validator state info.

Additional context
See related historical discussion in #3746, and recent PR in EventTombstoneValidator - #4277.

[conorsch]

Talked through the shape of these events with @plaidfinch and @cratelyn today. We want:

• catch-all state transition event: penumbra.core.component.stake.v1.EventValidatorStateChange, with fields:
  • validator identity key
  • new state
  • make sure all possible state transitions are accounted for: defined, active, inactive, jailed, tombstoned, enabled, disabled. check genesis states too (which may be earlier than the transition logic)
• new event: penumbra.core.component.stake.v1.EventValidatorDefinitionUpload
  • every time that a Validator definition is uploaded (which can happen in a variety of different states)
  • should include the entire definition
• missed-block event: penumbra.core.component.stake.v1.EventValidatorMissedBlock, with fields:
  • validator identity key
  • (this event is only emitted if validator was Active but did not sign)
• new events: penumbra.core.component.stake.v1.EventDelegate & EventUndelegate