Add function to estimate the rewards to be added to TACoRewardsDispenser contract

[manumonti]

The rewards to be pushed (transferred from bot to TACoApp contract) must be calculated/estimated.

As a first iteration and considering that this is intended to be used in TACo testnet, the rewards is being calculated following this expression:

rewardsToBePushed = AuthorizedOverall * APY * (secondsElapsedSinceLastPush / 1 yearInSeconds)
where:

AuthorizedOverall is the sum of the T authorizations of all stakes and can be queried as a public variable from TACoApp contract.
APY is the Annual Percent Yield for TACo staking rewards. Currently, 3.75%.