valset: update max_validators

[alpe]

There should be a way to update the maximum number of validators via gov proposal.
Not sure if OC or validator community would be responsible. 🤷

Solution (by Ethan):

1. Add optional arguments to the MigrateMsg. If set, while doing the migration, update the config. This will be used right away to demo in the testnet and as a recovery posibility.

pub struct MigrateMsg {
  pub min_weight: Option<u64>,
  pub max_validators: Option<u32>,
}

2. Add a new variant to ExecuteMsg - UpdateConfig, which just has those two fields for now. It must be gated so only admin can call it and it will update the config and save.

In another issue we expose this to the OC.

[maurolacy]

Agree. AFAIK, that's a setting that's defined in genesis, in the Blockchain, so doing that will involve some kind of privileged call from proposal's execution to the Blockchain. (This is wrong. This is enforced here:

poe-contracts/contracts/tgrade-valset/src/contract.rs

Line 600 in fe6d292

while !batch.is_empty() && validators.len() < cfg.max_validators as usize {

)

[kmw101]

I am not sure validators would agree an increase in the maximum as it would have an impact on their revenue? A compelling case would need to be made? Who would champion the increase other than new validators?

The OC are responsible for the allocation of EPs, and Punishing Validators not for the overall governance of the chain.

[ethanfrey]

I propose 2 approaches:

1. We add an optional field to MigrateMsg to allow setting this. We can do that when upgrading the contract in the testnet
2. We can add a new entry point on the valset contract that allows the OC to set a new max validators, and an OC proposal to do so.

We can use (1) to update the testnet-3 asap to demo this.
(2) can be a longer term solution and used in testnet-4 (once the app supports this proposal)