Proposal - Relabel username to display name and use email for local login.

[Neilk1021]

Currently we require the user to sign up with a unique username; however, there is nothing in the database that restricts users from having the same username. This logic is currently applied by our servlets when the user is creating an account, and all future login attempts require the user to sign in with that username.

Given there is nothing enforcing usernames to be unique past account registration it would make sense to opt for a different variable to represent user identity. Luckily, this is already solved: a user cannot have an active account without an email and every email must be unique. Therefore it makes sense for the user to login with their email rather than their username keeping it only for display purposes. Texera already follows the idea that email is identity as its how datasets resolve their save path and is the backbone of how sharing works.

Questions

1. Is there anything tied directly to the username's uniqueness that would break if we no longer enforce it to be unique at registration?
2. Should the registration for local login drop username's uniqueness requirements?