Establish test strategies for internal releases

Context

&1373 (closed) and &1201 (closed) aim to establish a new internal release strategy to remediate GitLab single tenant SaaS instances in case of high-severity incidents.

Establishes a new private release strategy involves many touch points, including:

• Creation of a new internal package type
• Modifications to project managed versioning (Omnibus, CNG) to adapt a new package type
• Modifications to Dedicated projects to be able to install a new package
• Establish a new internal release process end-to-end
• Modifications to release tooling to support a new release process

The purpose of this issue is to establish testing strategies for the many angles involved in internal releases

Exit criteria

Determine testing strategies for

• The internal release process end-to-end: Merging security fixes, merge-train, kicking off the internal release process, etc #20727 (closed)
• Creation of an internal release package: Omnibus and CNG builds, package available on the pre-release channel and dev registry #20726 (closed)
• Installation of a package on the Dedicated side. https://gitlab.com/gitlab-com/gl-infra/delivery/-/issues/20837