Support air-gapped (offline) Dependency Scanning for on-prem instances
### Problem to solve
Our gitlab~6703392 tools currently require internet connectivity to run using standard configurations. We should aim to support offline execution and provide clear documentation on how to configure scanners for such installations.
### Proposal
As Dependency Scanning is made of separate analyzers we need to address this issue for each of them:
- [ ] [bundler-audit](https://gitlab.com/gitlab-org/security-products/analyzers/bundler-audit)
- [ ] [retire.js](https://gitlab.com/gitlab-org/security-products/analyzers/retire.js)
- [ ] [gemnasium](https://gitlab.com/gitlab-org/security-products/analyzers/gemnasium)
- [ ] [gemnasium-maven](https://gitlab.com/gitlab-org/security-products/analyzers/gemnasium-maven)
- [ ] [gemnasium-python](https://gitlab.com/gitlab-org/security-products/analyzers/gemnasium-python)
From @fcatteau's [comments in parent epic](https://gitlab.com/groups/gitlab-org/-/epics/1359#note_174170622): currently, none of these would work without connecting the CI to the Internet.
epic