[CON/TP/Log-in]: Re-implement cross-platform log-in

[katamatata]

Context/background

After Salesforce integration, the cross-platform log-in feature doesn't work, and we want to re-implement it. Users with a TP jobseeker profile should be able to log in to CON with the same credentials (a mentee profile should be automatically created). And vice versa, users with a CON mentee profile should be able to log in to TP with the same credentials (a jobseeker profile should be automatically created).

What needs to be done?

The logic needs to go something like this:

1. User tries to log into CON and the front-end tries to load the ConProfile. Or, user logs into TP and the front-end tries to load the TpJobseekerProfile.
2. Back-end doesn't find ConProfile or TpJobseekerProfile
3. In this case, back-end tries to...
   a. for ConProfile, check if user has an existing TpJobseekerProfile. If so create a new ConProfile based on the data available in TpJobseekerProfile (a mapping)
   b. for TpJobseekerProfile ... vice versa
4. Return the newly created profile record

The appropriate place to insert this logic in the backend is the code that handles the first query that the CON or TP front-end tries to run to load the desired profile record.
Furthermore, refer to the old loopback cross-platform log-in code that handled this specific case. Look here for it: https://github.com/talent-connect/connect/blob/282df3b1d474efa1f4ada0f458b55f094073ed24/apps/api/common/models/red-user.js