Merge pull request #10422 from AlanCoding/quay_default

Make quay.io the registry URL default

SUMMARY
It's unclear what format the registry "Authentication URL" should be.

It's too late to change the strings because of translations, ping @rooftopcellist, but this change would clarify the format without adding wording.
ISSUE TYPE

Feature Pull Request
Docs Pull Request

COMPONENT NAME

API

ADDITIONAL INFORMATION
Seems to behave pretty good in the UI.

Reviewed-by: Jake McDermott <yo@jakemcdermott.me>
Reviewed-by: Jeff Bradberry <None>
Reviewed-by: Shane McDonald <me@shanemcd.com>
Reviewed-by: Bianca Henderson <beeankha@gmail.com>

awx/main/models/credential/__init__.py

@@ -1118,6 +1118,7 @@ ManagedCredentialType(
                 'label': ugettext_noop('Authentication URL'),
                 'type': 'string',
                 'help_text': ugettext_noop('Authentication endpoint for the container registry.'),
+                'default': 'quay.io',
             },
             {
                 'id': 'username',