We need two types of Registry clients, `docker` and `skopeo` while the
functionality to communicate/deal with Registries is the same.
Therefore, we parameterize a client type for this functionality.

- Use `skopeo` client instead of `docker` to login to Registry
  if the skopeo fetcher is used.

- Don't create additional `target` subdirectory so we get Target
  specific OCI store file/folder tree.

- Add insecure-policy` param to `skopeo copy` cmd in order to avoid a
  need in `/etc/containers/policy.json` file, which contains the same
  insecure policies by default.

- Python script to preload Apps within OE build.
- Auxiliary bash script that invokes the preload python script aimed to
  simplify the preloading running and debugging within container and OE.

Use a temporal file for authentication material in order to avoid a need
in access to `/run/containers` folder during the OE builtin preloading.

The OE-builtin preloader supports only "restorable" type of Apps,
therefore we need to pass the corrsponding param to the bitbake context.