Validator set preferences module

[ValarDragon]

Background

We should make a new module, for validator set preferences.

The goal is to give users & contracts a better UX for staking to a set of validators. E.g. a one click button, that stakes to multiple people. Then a user can set (or realistically a front-end provides) a list of recommended defaults. (E.g. governooors, relayers, chain/stack contributors, etc) This can technically be done off-chain today with front-ends, having preference lists stored locally. Having this on chain:

• eases front-end code burden that is already very high in cosmos
• reduces front-end lock-in, giving you the same UX across multiple front-ends

What this module should do is:

• Allow an address to set a list of {val addr, weight} in state, called their validator set preference
• Give users a single message to stake X osmo, according to their validator set preference distribution
• Give users a single message to claim rewards from everyone on their preference list (or should it be all their staking positions)
• If a user does not have a validator set preference list set, and has staked, make their preference list default to their current staking distribution
  • Expose a query for this
• If a user has no preference list and no staking, then return error for messages

Suggested design

couple minute initial sketch of a proto for this

message ValidatorPreference {
  string val_oper_address = 1 [ (gogoproto.moretags) = "yaml:\"address\"" ];
  // two options for how we build weight.
  // Either as a decimal between 0 and 1, and they all sum to 1
  // OR normal int, and percentage to each validator is int/total weight
  string weight = 2 [
    (gogoproto.customtype) = "github.com/cosmos/cosmos-sdk/types.Dec",
    (gogoproto.moretags) = "yaml:\"autostake_rate\"",
    (gogoproto.nullable) = false
  ];
}

message ValidatorSetPreference {
  repeated ValidatorPreference preferences = 1 [ (gogoproto.nullable) = false ];
}

Acceptance Criteria

• Above listed features built out
• We follow a module standard similar to x/TWAP (we should do so for new modules going forward)
• We document what rounding behavior for splitting stake amounts across validators were taking. Any particular decision is fine, just need to document / be clear about what we did