[Feat] BoosterOwnerSecondary, Stash3.2 and new PoolManager

[phijfry]

Changes

There are 2 core changes in this PR:

1. changing the implementation of the ExtraRewardsStash in order to handle secondary reward tokens in a more robust manner by wrapping any transfers in a StashedToken to avoid potential overflows. This is locked in by consequently sealing off (or adding the ability to seal off) changes to the Stash via a new BoosterOwner.
2. locking off the forceAddPool function on the PoolManagerSecondary by changing the operator from PoolManagerV3 to PoolManagerV4. This function is unused and could potentially cause issues if mishandled.

Technically speaking, this PR

Implements file changes from https://github.com/aurafinance/convex-platform/pull/49/files , notably changing the ExtraRewardStashV3 implementation for future pools.

PoolManagerV4 and BoosterOwnerSecondary diffs:

• PoolManagerV3/4 https://www.diffchecker.com/HcULPGwU/
• BoosterOwner/Secondary https://www.diffchecker.com/NdiJyJsp/

Implementation

This upgrade can be rolled out in a single governance transaction using the steps tested in https://github.com/aurafinance/aura-contracts/pull/160/files#diff-5bba4aa750b2bce458f684224340afd8f6205c970dc4e9ff02c83476a13a5af1

This Stash will then be deployed for all pools added to the system after the multisig transaction, and the BoosterOwnerSecondary will be sufficiently blocked off from all previous pools as shown in the setStashExtraReward function