WIP: Add instructions for SAST DinD in offline environments

What does this MR do?

Adds instructions for running SAST in limited internet access environments with DinD (docker-in-docker).

Screenshots

not applicable

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

was tested in #11520 (closed)