Adds management command to find possible username conflicts

[jkachel]

Pre-Flight checklist

• Testing
  • Code is tested
  • Changes have been manually tested

What are the relevant tickets?

#259

What's this PR do?

Adds a management command to identify usernames that would conflict after normalization. This is step one of the process for resolving #259.

The management command is find_username_conflicts and running it will load all user IDs and usernames from the database and run through them to see if a normalized username would be generated more than once. If the normalized username would be generated more than once, it outputs that normalized username with the IDs of the users that would cause a conflict. These can then be manually edited (in Django Admin or in the database directly).

The command does not change usernames at all and the standard caveats apply to modifying usernames manually - they will need to be modified on the Open edX side as well.

This command will need to be run and the affected accounts adjusted before #627 can be merged, as it adds a uniqued normalized_username field and automatically normalizes existing usernames.

How should this be manually tested?

Create two users: their usernames should share spelling but one should contain accented characters where the other doesn't. (For example, taylor and tâylör.) Then, run the find_username_conflicts command. It should identify those two accounts specifically as accounts that may conflict after normalization.

[briangrossman]

@jkachel

Is it correct that the process will be:

1. While find_username_conflicts returns conflicts:
   • Manually update MITx Online usernames
2. Merge Adds username normalization #627
   ?

Note that the steps to update an MITx Online username are:

• Update the username for the user record in the MITx Online admin
• Update the username for the user record in the MITx Online Open edX admin
• If the learner has a Micromasters account:
  • Update the username (UID) for the user's social auth in the Micromasters admin (the mitxonline one, not the edX one)

[jkachel]

@briangrossman yes, that'll be exactly the process I had in mind and should prevent #627 from failing to deploy successfully. (One of the migrations in there will automatically normalize the incoming usernames and it'll fail if it hits a conflict.)

[arslanashraf7]

@jkachel Can this PR be reviewed independently or it should be reviewed after #627?

[jkachel]

@arslanashraf7 this actually needs to be reviewed/merged before #627

[arslanashraf7]

I tested it with the following cases:

• Create normal users (No results)
• Create a user with a normal username and then a user with some accented character in the same username (Outputs usernames & ids)
• Create a user with accented characters based username & then a new user with a normal username without accented chars (Prints ids of the conflicts)
• Above step with multiple users with the same username but different accented chars (Prints multiple IDs of those users)

For more readability, we could print email ids too for the conflicted users because even the usernames would be the same considering accents the email ids might be different. But I'm okay with this since this looks more like a one-timer.

Looks good 👍