[SL-3069] Expose a way to disable automatic date_trunc on time dimensions

[Jstein77]

Summary

MetricFlow will apply a date_trunc on time dimensions to make sure they conform the the specified granularity. i.e we will render this SQL for the following dimension date_trunc('day', data_dt)

- name: data_dt
        type: time
        is_partition: True
        type_params:
          time_granularity: day

The issue is that Snowflake, and likely other engines, won't respect partition pruning on data_dt if we apply a date trunc function. We need a way to respect partition pruning for time dimension

Possible Solutions

We could expose a way to make the date trunc function optional i.e

- name: data_dt
        type: time
        is_partition: True
        type_params:
          time_granularity: day
          enfore_granularity: false #default true 

This could lead to some odd behavior with time based joins, where we expect every dimension to conform to the specified grain. The expectation would be that the user makes sure the dimension is add the right grain downstream to guarantee all time based joins will work.

_{From SyncLinear.com | SL-3069}