Allow override of initial account activation from address.

In PR #15030, we missed adding the override of the initial account activation from address using the ACTIVATION_EMAIL_FROM_ADDRESS SiteConfiguration setting. We had only added the override when a subsequent activation email was sent.

ENT-318

common/djangoapps/student/views.py

@@ -619,10 +619,8 @@ def compose_and_send_activation_email(user, profile, user_registration=None):
     # Email subject *must not* contain newlines
     subject = ''.join(subject.splitlines())
     message_for_activation = render_to_string('emails/activation_email.txt', context)
-    from_address = configuration_helpers.get_value(
-        'email_from_address',
-        settings.DEFAULT_FROM_EMAIL
-    )
+    from_address = configuration_helpers.get_value('email_from_address', settings.DEFAULT_FROM_EMAIL)
+    from_address = configuration_helpers.get_value('ACTIVATION_EMAIL_FROM_ADDRESS', from_address)
     if settings.FEATURES.get('REROUTE_ACTIVATION_EMAIL'):
         dest_addr = settings.FEATURES['REROUTE_ACTIVATION_EMAIL']
         message_for_activation = ("Activation for %s (%s): %s\n" % (user, user.email, profile.name) +