feat(vpool): maintenance margin ratio should be modifiable by governance

[NibiruHeisenberg]

Task Summary

• [x] Since maintenance margin ratio is an attribute of a Vpool, it can be removed from the genesis.
• [x] Add tx to edit vpools

[Unique-Divine]

Suggestion

We should make this a parameter of the virtual pool rather than the module. It's common for different asset pairs to have different maintenance margin requirements and maximum leverage on larger exchanges. Different position change magnitudes can also factor into this.

Benchmark - Binance

Pair	Tier	Max Leverage
BTC/USDT	1	10x
BTC/DAI	1	3x
AAVE/BTC	1	5x
BNB/USDT	1	10x
DOT/BUSD	1	5x
ATOM/ETH	1	3x
ATOM/BUSD	1	5x

References:

• Isolated Margin Data Tables. Binance. | (current leverage tiers)
• Updates on Leverage and Margin Tiers of Binance Futures Contracts (2021-08-18). Binance.

Benchmark - dYdX

Asset	Leverage Limit
BTC	20x
ETH	20x
All Other Markets	10x

Reference: Maximum Leverage for Perpetuals. dYdX

Benchmark - Huobi

"Huobi Futures support 1x-100x leverage"

Reference: Contract Leverage Introduction

@NibiruChain/backend

[matthiasmatt]

It's already a parameter for the vpool (#729)

x/vpool/keeper/pool_state.go

// CreatePool creates a pool for a specific pair.
func (k Keeper) CreatePool(
    ctx sdk.Context,
    pair common.AssetPair,
    tradeLimitRatio sdk.Dec, // integer with 6 decimals, 1_000_000 means 1.0
    quoteAssetReserve sdk.Dec,
    baseAssetReserve sdk.Dec,
    fluctuationLimitRatio sdk.Dec,
    maxOracleSpreadRatio sdk.Dec,
    maintenanceMarginRatio sdk.Dec,
    maxLeverage sdk.Dec,
) {
    k.Pools.Insert(ctx, pair, types.VPool{
        Pair:                   pair,
        BaseAssetReserve:       baseAssetReserve,
        QuoteAssetReserve:      quoteAssetReserve,
        TradeLimitRatio:        tradeLimitRatio,
        FluctuationLimitRatio:  fluctuationLimitRatio,
        MaxOracleSpreadRatio:   maxOracleSpreadRatio,
        MaintenanceMarginRatio: maintenanceMarginRatio,
        MaxLeverage:            maxLeverage,
    })

    k.ReserveSnapshots.Insert(
        ctx,
        collections.Join(pair, ctx.BlockTime()),
        types.NewReserveSnapshot(
            pair,
            baseAssetReserve,
            quoteAssetReserve,
            ctx.BlockTime(),
        ),
    )
}

[matthiasmatt]

Ideally all parameters of a vpool (along with the k value) should be adjustable by governance.

I'm wondering if we want to have k slowly adjusting from A->B on a timeframe? Curve does it for their amplification parameter on their stable pools, osmosis does it for their weight change in LBP.

[NibiruHeisenberg]

The objective of this ticket would be to move the vpool fields into the module params so that they are subject to governance proposals. Right now I don't believe there is a way to modify the vpool fields after the chain goes live.