Is your feature request related to a problem? Please describe.
Related to #2526, we need to support user account deletion. When a user requests to have their account deleted, we do not have an effective way to do so short of direct database access.

Describe the solution you'd like
Users with admin-level access can have a select option under https://tasks.hotosm.org/manage/users/ to delete an account. There should be a dialogue to confirm deletion.

On the backend, the solution should be designed to remove the users personal information without deleting core TM data/functionality like task history. Replace user ids with [Deleted user] in comments and such. We will need to decide how to effectively remove account information to comply with GDPR.

Additional context
We have received requests for account deletion in the past, and have not come to a sufficient solution to comply with these requests.