Adds username normalization

[jkachel]

Pre-Flight checklist

• Migrations
  • Migration is backwards-compatible with current production code
• Testing
  • Code is tested
  • Changes have been manually tested

What are the relevant tickets?

#259

What's this PR do?

Fixes #259.

This adds a normalized_username field to the users model and an API function to perform the normalization. It also updates the openedx create_edx_user call to pass the normalized_username field instead of the regular username field.

How should this be manually tested?

The migrations to add the normalized_username field will automatically normalize the usernames. Because of that, it's pretty important that your user database does not contain accounts that will conflict. (Per #259, the normalized_username field is uniqued.) There is a management command to check for and fix usernames that would conflict that's in PR #629.

After performing the migrations, create a user with a username using accented characters (áüô, etc.). The username should be created on the Open edX side with those characters converted to non-accented characters (auo, etc.).

Some characters will not be normalized and will instead be dropped. This includes ø so testing with that character will result in a normalized username without that character (for example, Søren will normalize to Sren).

[annagav]

Just a minor comment

[annagav]

Is this a duplicate of the test in the api.py? Is this test incomplete?

[jkachel]

Should be fixed in ea43e81 - this was old and got left by mistake

[annagav]

👍

[pdpinch]

@jkachel can you remind me why you put this on hold?

Would this have avoided the situation in https://odl.zendesk.com/agent/tickets/139242 and https://sentry.io/organizations/mit-office-of-digital-learning/issues/2616447470/events/9ab540c0d80f4983933e71bb7b9cd728/?project=5864687

[jkachel]

@jkachel can you remind me why you put this on hold?

Would this have avoided the situation in https://odl.zendesk.com/agent/tickets/139242 and https://sentry.io/organizations/mit-office-of-digital-learning/issues/2616447470/events/9ab540c0d80f4983933e71bb7b9cd728/?project=5864687

This was put on hold because it needed some coordination to do - there was a part to this that was normalizing the existing usernames in the database. (See #259 (comment)) This was done about the time Brian left, though; I was going to get him to help with that. Otherwise, the code worked and it would have caught this, I think. It'd need some revising to work in the current version of the app before we could deploy it now.