Create the resolvers for updating the user data

[flacial]

Problem

We're in the process of making it possible for the students to update their info, such as their username or password. Currently, there's no way to do that because in the backend side, the resolvers for updating the data are missing.

Steps to reproduce

1. Go to the resolvers
2. Observe that there are no resolvers for updating the user info

Expected behavior

The backed should have the resolvers for updating the user data info

Actual behavior

There is currently no way for users to update their info by calling a resolver

Solution

implement GraphQL resolvers for updating user data (username, firstName, lastName, password) in the database. This will allow us to specify the logic for updating user data on the server, which can then be called by the client to make updates.

Additional context

• Related to #1629

[flacial]

Closed in #2656