Depeg trigger

[pooleja]

This PR adds a trigger when to start charging the increased fee.

In practice, smaller pools with lower TVL are being routed trades as they charge a lower fee whenever users are selling ezETH. Since ezETH maintains a small depeg during normal market environments, this will allow the pool to compete during those periods.

TODO:

• Discuss whether the trigger and other vars should be configurable
• Discuss whether we should make the hook upgradeable to prevent the need for TVL migration if we want to make changes in the future.