Check for invariants - epic

[alpe]

This issue is to discuss an on chain safety net that secures tokens and important data

Background:

In the Cosmos-SDK modules can register for a callback to verify that their state is consistent. On any failure the chain is stopped by a panic (in the crisis end blocker). These operations run with an infinite gas meter and do ensure data integrity.

I think we have a similar use case in our contracts. For example
the amount locked in the valset contract must not be < sum of all staked amounts and pending claims.

Steps can be

• Identify and document relevant conditions that will always be true

• define how a callback should be handled by a contract:

  • should it check it's owns state only or also be able to query other contracts/ native modules?
  • how would the callback message look like?
  • runs in a read only context

• Add a new privilege to tgrade (check_invariants for example) with sudo call to registered contracts

  • should we integrate with crisis or do in own end blocker?