Group audit updates

[amstilp]

Right now we are getting audit errors for some groups that we added to the app manually (via the admin interface), but are not members of. To fix this, we can have a new field for ManagedGroup that tracks whether the app is a member. This field should be true by default.

• Add a field to ManagedGroup with default True
• In the audit for managed groups, do not report errors for groups that have has_app_as_member=False
• Add an email field for the group instead of directly constructing it. Some groups' emails are not the group name with @firecloud.org appended.

[amstilp]

We may not need the has_app_as_member field if we store the group email.