✨ Implement a state for indicating if proving scheme is enabled

[hacheigriega]

✨ Feature

This issue calls for a mechanism for checking if a proving scheme is enabled and storing the boolean state in x/pubkey.

• Inside the x/pubkey end block, check the proportion of validators that have registered a key corresponding to a given proving scheme.
• There will be a boolean state that indicates if a proving scheme is enabled. This state will default to false until the end block check passes. This state will be used by:
  • vote extension handlers to check which proving schemes are active
  • create-validator and unjail transactions as described in ✨ Gatekeep validator set from validators without required SEDA keys #422