Taking this shortcut has two benefits:

1. It allows charts to be fetched from AWS's public container registry
   at public.ecr.aws
2. It makes reconciling a HelmChart faster by skipping one or more
   potentially expensive API calls to the registry.

I adapted the unit tests to the new behavior that the
OCIChartRepository doesn't fail anymore for the case where a specific
chart version has been requested that doesn't actually exist in the
registry.

refs #845

Signed-off-by: Max Jonas Werner <max@e13.dev>
Signed-off-by: Sunny <darkowlzz@protonmail.com>