Refactor `tiers` to include `multipliers` instead of `mintAmounts`

[CruzMolina]

Likely involves: - expanding tiers to be a single level mapping with a collection address as the key - expanding setTiers to support setting tiers for each collection address

• swap out tierMintAmounts for tierMultipliers from TiersData
• add getters/setters/events for collectionPriceToMintRatioBP
• rework _resolveMints consolation tier selection logic

[NouDaimon]

This may be what we want - Daniel said it may be some function based on collectionMintPrice.