[Woo POS] Consider in-memory storage for product selector, independent from store management mode

[samiuelson]

Separating products' data layer from store management mode would allow performing full sync of products including wiping stale data on "pull to refresh" or during initial data loading.

[dangermattic]

🚫 Please add a type label (e.g. type: enhancement) and a feature label (e.g. feature: stats) to this issue.