Track price changes on per-user basis

Problem/Motivation

Currently, the module only tracks how the price changes for an anonymous user. If the merchant is required to show how the price changes for each user, this cannot be achieved. However, the price history entry has a commerce context value data object registered, therefore it is possible to distinguish price history per user.

Some things to consider:
- is it only a theoretical feature or is there a merchant asking for it,
- should it be opt-in, opt-out, or default,
- this asks for much more data - what should be considered? Indexes?

Proposed resolution

TBD

Remaining tasks

TBD

User interface changes

n/a

API changes

n/a

Data model changes

TBD