Refactor use of getUserDto schema between functions

[annarhughes]

Is your feature request related to a problem?

Most of our backend api requests are related to users, so before the request function is run, we get the current user from the database and make the user data available in the request and following functions. The problem is that we are passing around the user data in a serialized schema GetUserDto and instead we should be using the pure UserEntity schema/types, for all internal functions. GetUserDto schema should only be used to serialize user data before returning the response, i.e. in the controller

Describe a solution:

• Remove user from the request context - we are aiming to use userEntity instead - see FirebaseAuthGuard.tsx and getUserByFirebaseId function in user.service.ts
• Replace all uses of req['user'] in controllers, instead using req['userEntity']
• Remove all uses of GetUserDto from our functions/service files, instead using UserEntity type
• Fix any related issues - running yarn test and yarn lint will help discover issues
• You should also run Cypess tests to ensure this doesn't break anything in the frontend.
• This is a large issue so you may want to break down into smaller issues

This is the first step (see #454) in improving the maintainability and performance of the API and how it handles users. The cleaner typing will help future contributors understand the code!

Additional context and resources:

Tests may need to be fixed following this update - run to check failing tests

Ticket breakdown

#547
#546
#545

[eleanorreem]

I am going to break this down into bitesized chunks as I think this refactor will be too mammoth on its own. I have linked above