OSC-1.6.0: update the upstream_sources.yaml for the osc-operator

(Requirement: Initial branch structure should be ready for the current release. So this issue could be blocked if that is not in place already).

sandboxed-containers-operator upstream Github repository is consumed by osc-operator and osc-must-gather components.

Currently, we are releasing those components from the main branch. But please always double-check with our "OSC Releases: Dependencies and refs" what reference was decided for the current release. This document should be our source of truth.

Since we consume this repository directly from the upstream branch, there is no need to update midstream fork, only the midstream CPaaS configuration files:

  1 . Make sure the sandboxed-containers-operator, section is pointing to the right branch/commit (as defined at our document mentioned above). If not, send a MR to this repository. Pay attention to the target branch name. Branch name should match the upcoming release. I.e: osc-1.6-rhel-9 if we are preparing for the 1.6 release.

  2. Make sure the `distgit/containers/osc-operator/Dockerfile.in` is matching what we need. Usually we need to ensure we are using the right container base image and that the steps used to build this image are matching upstream as close as possible. 

3. Do the same for `distgit/containers/osc-must-gather`.

Notes:

  1. `Dockerfile.in` and `upstream_sources.yaml` are related and need to be in sync. For instance, sometimes upstream changes the repository structure or renames files and folders. If we are using a new version with this new structure, the Dockerfile should be able to use the right paths to build the image.
 
  2. Ideally this Dockerfile.in should be in sync with the upstream. Changes to the upstream should be also incorporated to this file and the step 2 and 3 would be just a quick verification.

Remember that our build system is offline so we are building in "offline mode" with the Cachito help.