Prop 404: Incentivise Core StableSwap pool: USDC/USDT/BUSD

This proposal recognises the StableSwap 3pool of USDC/USDT/BUSD as a core StableSwap pool and enables OSMO incentives at the next routine incentives proposal.

## Details
This is a signalling proposal to include the StableSwap 3pool USDC/USDT/BUSD into the set of pools that receive OSMO liquidity incentives by recognising it as a core StableSwap pool.
After this proposal has passed governance, the pool will be added to the regular incentives program of OSMO and receive incentives as a Stable/Stable pool.

The pool incentivised at this time would be Pool 877 with all assets listed provided via the Axelar bridge and as such are the canonical representations of these on Osmosis according to Proposal 206. If the canonical status of one of these assets is changed then incentives would move at the next routine proposal to the pool containing the new canonical assets, with the highest volume and matching the criteria stated in Proposal 377.

Stable pools are incentivised by the model defined in Proposal 377. In brief, incentivised pools receive a subsidy of up to 2 times the value of fees generated in the pool in OSMO, with the total of the Stable/Stable category being capped as 4% of current Liquidity Provider emissions.

This proposal depends on the passing of Proposals 402 and 403, which recognise USDT and BUSD as Stablecoin assets on Osmosis. If this proposal passes whilst one of the referenced proposals fail then it would have no immediate effect as one of the constituent assets would not be recognised as a Stablecoin asset. If all constituent assets become recognised by Osmosis governance as Stablecoin assets in future then this proposal would take effect.

## About USDC
USDC is a stablecoin redeemable on a 1:1 basis for US dollars, backed by dollar-denominated assets held in segregated accounts with US-regulated financial institutions and issued by Circle.
Website: https://www.circle.com/en/usdc
## About USDT
Launched in 2014, Tether was the first stablecoin issued and remains the most prevalent stablecoin in use across the crypto ecosystem.
Website: https://tether.to/

## About BUSD
BUSD is a 1:1 USD-backed stablecoin approved by NYDFS and issued by Paxos on Ethereum. Binance provides Binance-Peg BUSD on other chains by locking an equivalent amount of assets on Ethereum. The current version of BUSD in use on Osmosis arrives from Ethereum via the Axelar bridge.
Website: https://paxos.com/busd/

Commonwealth Thread: https://commonwealth.im/osmosis/discussion/9353-incentivise-core-stableswap-pool-usdcusdtbusd