Update Omnibus project to support internal releases notation

Context

There is an emerging need to build and deliver private packages to remediate GitLab Dedicated instances, the internal nature of such packages is required to prevent disclosing the vulnerability and to make it independent from the GitLab patch releases.

The outcome of the tag and tagless investigation showed the Omnibus project doesn't support an internal notation (17.5.1.internal0) https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20504#impact-per-project. This issue aims to adjust the Omnibus codebase to support internal packages.

Links:

• https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20565+
• https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20504+
• https://gitlab.com/gitlab-org/distribution/team-tasks/-/issues/1626+

Exit criteria

Collaboration with the Build team (former Distribution) will be required

• Identify the changes required on Omnibus
• Distribution maintainers are aligned with the required changes
• Adapt Omnibus pipeline’s workflow for internal releases so that:
  • gitlab-org/omnibus-gitlab!8045 (merged)
  • gitlab-org/omnibus-gitlab!8051 (merged)
  • the pipeline excludes QA-branch job
  • it only builds Ubuntu images in the package stage
  • it only uploads Ubuntu images to the pre-release channel
  • the check-packages-functionality job to only check Ubuntu images
  • Use the internal release notation for deb packages
• [-] A test is performed to validate the Omnibus project supports internal packages - split to #20783 (closed)