Store dates from cron "as-is", remove time conversion from cron

[jonespm]

Thank you for contributing to this project!

Describe your problem or feature you'd like added

It was noted on some recent fixes like #1484 that MyLA is storing values in local time. We had some discussion that this probably isn't needed and the application could do the conversion in the API (either in GraphQL or in the view) to the value in the settings. This might require some minor migration or we can just require dropping the tables and re-running the cron.

This would probably be made easier if the old assignment view API's were removed #1492 and the cron for the UDW #1493 was also removed.

[jennlove-um]

Use the LTI launch timezone value to detect it. Another option would be to use the browser timezone, but LTI is the best approach since it will match the timezone in Canvas.

[jennlove-um]

@jaydonkrooss Assigning you as an observer on this one.

[pushyamig]

Here is the time zone related change with newest Django 4 upgrade.
https://docs.djangoproject.com/en/4.2/releases/4.0/#zoneinfo-default-timezone-implementation

[lsloan]

I recommended this issue to Jaydon. He can discuss it with me as he makes progress with it.

[jaydonkrooss]

From what I've been gathering on the previous issue #1484, it seems that we're not trying to have any more local time conversions when populating the MyLA database, instead putting the conversion client-side. Based on this commit for that initial timezone fix, I'm thinking the only fields we care about in this case are local_date from assignment and grade_posted_local_date from submission. It seems that other datetimes are being imported from UDP without conversion; please share if there are other fields I'm not aware of that I should be looking at.

Specific changes I'm considering:

1. drop the local_date field and use already provided due_date on the frontend
2. edit the grade_posted_local_date to simply be grade_posted without a local time conversion
   (I'm not sure if this field is even used on the frontend so I don't anticipate any UI regression we'd have to test)

[jennlove-um]

Cron runs fine and no issues detected in beta testing.