Update veFXS boost to catch up with rising FXS price

With the rising FXS price it becomes ever harder to enable a full farming boost.

With the current FXS price at 5$ people are required to lock up 5$ value for 4 years in order to boost 2$ worth of LP. This asymmetrical ratio will only increase with further growth of the FXS price.

As this continues people will be less inclined to buy and/or lockup FXS (Risk/Reward is simply not worth it anymore).

My proposal is to adjust this ratio to decrease the current asymmetry.

I have sketched out a couple scenarios at the current FXS price of 5$:

3veFXS per 1 FRAX = 5$ locked up for 4 years boosts 2.66$ worth of LP.

2.5veFXS per 1 FRAX = 5$ locked up for 4 years boosts 3.2$ worth of LP.

2veFXS per 1 FRAX = 5$ locked up for 4 years boosts 4$ worth of LP.

We can eventually find a way for this to be automatically adjusted in accordance with the fluctuating FXS price.