[SIP-02]: nUSD Fees Rework

Full Context: https://forum.synapseprotocol.com/d/2-sip-02-nusd-fees-rework/

Proposal

Enable "interactive admin fee" for the ETH Nexus pool and the base stable pools on other chains. Update fees for swapping/bridging.

1. Enable following initial admin fees: ETH/Arbitrum: 90% BSC/Poly/Ava/Fantom: 100%

2. Reevaluate admin fee for each base pool on weekly basis based on the pool's LP virtual price (VP). VP_new < min(VP_old, 1.0005) ===> decrease admin fee VP_new > max(VP_old, 1.0005) ===> increase admin fee

3. Set following swap/bridging fees: a. 0.03% = swap fee for the "base pools" (nUSD pool on ETH, USD-LP on other chains) b. 0.04% = swap fee for metapools (nUSD pools on other chains). c. 0.04% = bridge fee for nUSD from any chain to any chain (with the same minimum amount depending on the receiving chain as it now).