Support for date_part for Dimension & TimeDimension

[DevonFulcher]

Description

This PR adds support for the date_part for Dimension & TimeDimension. This is helpful for our Tableau integration. A time_dimension_call_parameter_set is now created if Dimension(...).grain(...) or Dimension(...).date_part(...) is used or both.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• This PR includes tests, or tests are not required/relevant for this PR
• I have run changie new to create a changelog entry

[tlento]

Let's not add support for WEEK here, I'll just need to remove it again later. And we might want to update the docstring on the DatePart enum to indicate the reasoning.

Otherwise, this looks good to me!

[QMalcolm]

This looks great! Some other people left comments on some things to add / change, and I don't have more to add.

Separately, I noticed that the issue in the changie doc is listed as None. Can we start creating issues for this kind of work moving forward? We have a nice template for this kind of internally motivated work. Having the issue is helpful for when we generate the release notes with changie. Having the issue in advance gives us in core an idea of whats coming down the pipe.

Additionally, is this going to need to be backported and put into a 0.3.latest patch release? If so we need to plan this work on the core side. Again, having a DSI issue will help with this.