feat: adding new api endpoint to handle user retirement

[DonatoBD]

Description

Since the ecommerce is deprecated and will be maintained in redwood, this PR was directly made to the NAU fork to add an API endpoint to ecommerce that performs user retirement.

For this, the endpoint /api/v2/user/retire. was added, taking advantage of the fact that the function already exists in edx-platform.

As the ecommerce did not store user profile information, this API deletes the social_auth associated with the LMS and modifies both the username and email of the user to comply with the same pattern as in LMS. In this way, the user will be considered retired, and we can compare it with the LMS data if needed to understand how it reached that state.

Regarding validation at the time of authentication, I do not consider it necessary to add a conditional that checks if the user is retired or not, since the ecommerce authentication works via SSO using the LMS and this validation already occurs for retired accounts in the LMS.

If you need to remove or change any user-related data (PII), we can add it to this API to be processed during user retirement process

Testing instructions

1. Build an ecommerce image with the branch worked on this PR
2. Install tutor-contrib-retirement fork with the branch worked on that PR
3. Run a tutor local environment with ecommerce, discovery and retirement activated
4. Declare COOL_OFF_DAYS to 0 so you can test the retirement workflow without wait 30 days (or modify the retirementstatus record directly through mysql)
5. Register, go to account and delete you account
6. Run tutor local retire-users to check the entire retirement workflow

[igobranco]

LGTM ✔️