Seed Gauge System: add view function for subgraph.

[Brean0]

When a user calls getLockedBeans in the same block as the sunrise block, the function returns an empty array, due to the lockedBeans implmentation using a twaReserves and the inability to calculate the twaReserves when no time has passed. Implementing an alternative where the current reserves were used would lead to an inaccurate amount.

This PR adds getLockedBeansFromTwaReserves, which allows the user to input a cumulativeReserves and timestamp. In practice, this can be used at the sunrise block by using the cumulativeReserves emitted by the WellOracle Event and timestamp of the previous season.

The view function was added to beanstalk.

function getLockedBeansFromTwaReserves(
        bytes memory cumulativeReserves,
        uint40 timestamp
    ) external view

• add view function for subgraph.