[Woo POS] Coupons: Unify`ProductFilterOption` and `VariationFilterOption` into a single filter option

[AnirudhBhat]

We have different enums for providing filtering options for Products and Variations. The goal here is to have a single filterOptions enum that could handle all the filters so that we could use it in our refactored business logic to fetch Products and Variations from data source.

[dangermattic]

Thanks for reporting! 👍