Add dependency proxy with group SAML

What does this MR do?

This test is an integration of two features: group SAML and the Dependency Proxy. The motivation behind this test is described at the raised bug: Dependency proxy does not work when SSO is enabled

Most of the code is re-used from the existing qa/specs/features/ee/browser_ui/1_manage/group/group_saml_enforced_sso_new_account_spec.rb, specifically the setup of the group. The instance is not using https and this is the cause of using the --insecure-registry flag.