[BIP-19] - BAC Vault New Strategy

Authors: @韦恩-Wayne, @qa1q, and the DEV team

BIP-18 BAB Redemption Pool is opened for the first time at UTC 00:00 5th Sep. 2021.

We have redeemed 818,870 BAB with 150,449 BAC.

For October, we will need to redeem more BAB to further mitigate the debt of the protocol.

As preliminary mentioned by BIP-18 BAB Redemption Pool, change the BAC Vault strategy to allocate a portion of its profit into Redemption Pool for BAB redemption is essential.

So our proposal for BAC Vault new strategy would be:

• When BAC is below $1, a portion of the BAC Vault profit will be allocated to Redemption Pool.
• The portion will be dynamic according to BAC_Price, maximumly 30%.
• PortionBACVaultToRedemptionPool = 30% * ( 1 - BAC_Price ).
• Auto harvest feature will be added to avoid the sandwich attack.

We will pause the BAC Vault manual harvest until this BIP is implemented (less than 1 week) if the snapshot vote is passed.