feat(TPA): Add middleware to handle TPA exceptions

[MoisesGSalas]

Description

During the third party authentication process there are some errors that are not correctly handled and result in a misleading 500 error page.

As far as we know, this issue happens under any of this three conditions, so far:

1. The connection with the Identity Provider (IdP) results in an HTTP Error. See social_core/backends/base.py
2. The pipeline step safer_associate_by_email raises EoxTenantAuthException when trying to associate a staff/admin account or when an account with the same email already exists. This is because EoxTenantAuthException doesn't inherit from SocialAuthBaseException.
3. If the step safer_associate_by_email is not defined in the pipeline a database IntegrityError is raised due to conflicting emails.

To solve the issue a new middleware class was created that process this exceptions and passes the correct AuthException to the next layer in the middleware chain.

Testing Instructions

1. To test (1) configure your OIDC provider such as that OIDC_ENDPOINT points to the wrong url.
2. To test (2) try to login with an IdP that returns the email of an account with staff/admin access.
3. To test (3) try to login with an IdP that returns the email of an account that already exists without defining safer_associate_by_email in the pipeline.

Aditional details

The error message should look like this:

[mariajgrimaldi]

Can you add a before and after screenshot?

[MoisesGSalas]

@mariajgrimaldi Can you add a before and after screenshot?

The before screen is a regular 500 error page. I added a screenshot with how the error message is displayed.