refactor: inherit from social auth exception

This change the heritance of the eox-tenant-auth-exception.

This with the purpose of the exception to be handled by the social tpa middleware exception
process.

You can see here that the new class is also based in value error exception.
https://github.com/python-social-auth/social-core/blob/29cbbd22b98d81d569a886b1cc0bd9a316cd124f/social_core/exceptions.py#L1

But the change is related with this PR:
eduNEXT/eox-core#171
So now as the exception is family  of the SocialAuthBaseException.

The the tpa middleware could managed it.
https://github.com/python-social-auth/social-app-django/blob/5.4.0/social_django/middleware.py#L35

Keep in mind that this middleware is parent of edx-platform middleware.
https://github.com/openedx/edx-platform/blob/ebcbe1cd9208191c0589d7fe538c6ac13470abe6/common/djangoapps/third_party_auth/middleware.py#L18

eox_tenant/pipeline.py

@@ -2,8 +2,13 @@
 The pipeline module defines functions that are used in the third party authentication flow
 """
 
+try:
+    from social_core.exceptions import AuthFailed
+except ImportError:
+    AuthFailed = Exception
 
-class EoxTenantAuthException(ValueError):
+
+class EoxTenantAuthException(AuthFailed):
     """Auth process exception."""
 
     def __init__(self, backend, *args, **kwargs):