Fixes #8375 - Not validating tag uniqueness per image

Images can have duplicate tags as images are shared across repositories. For
example, two repos could have a "latest" tag for an image.
Fixes #7647: Added support for external registries
Fixes #8226 - Support environment variables creation
fixes #8716 auto_complete helper now has a unique name.

Previous implementation overwrote the helper defined in foreman,
which in turn disabled auto completer for all search fields.
Refs #8717 - Fix cop line too long
Fixes #7647: Added support for external registries
Fixes #8393: added support for basic auth for standalone registries