Support Pre-aggregation incremental refreshKey with different time dimension than cube timeDimension

**Is your feature request related to a problem? Please describe.**
When using incremental pre aggregation building, with update window, we are forced to use the "official" time dimension of the cube(Lets call it "start_time". This is good for most cases, but when i want to import old data with old "start_time" i can't pre-aggregate it and i'm forced to change the refresh key manually.
this is because old start_time is not in in update_window.

**Describe the solution you'd like**
My suggestion is to add an option for different sql column to be used for update window sql(lets call it "insertion_time").
in this case you can import data with any date, and it will build the relevant pre aggregations.

**Describe alternatives you've considered**
Support "sql" property for updateWindow refreshKey.

**Additional context**
Mostly in slack when people ask about this problem, answer is change you refresh key, import the data and then change it back to original state.