Improve support for offline Code Quality scanning

Problem to solve

Add better, easier, offline scanning support for code quality scanning.

Intended users

Customers running GitLab in air-gapped, offline environments, especially within the DoD.

User experience goal

Eliminate the need for a user to compile their own Code Climate Docker image to run the scans totally air-gapped.

Proposal

Per @sololegends in gitlab-org/ci-cd/codequality!13 (merged):

Cleans up the CODECLIMATE_IMAGE variable for more obvious flow and readability. (No change in function)

Also adds an environment variable pass through to the codeclimate image for setting the engine docker image prefix. The variable to be passed through is CODECLIMATE_PREFIX. Which is the prefix for all docker pull ${engine} calls.

This will eliminate the need for a user to compile their own Codeclimate docker image to run the scans totally air-gapped.

NOTE: This merge will be dependant on this codeclimate pull request

Permissions and Security

TBA

Documentation

What does success look like, and how can we measure that?

TBA

What is the type of buyer?

Customers running Starter and above, operating in secure, offline environments.

Is this a cross-stage feature?

Not foreseeably.

Links / references

Customer requests

Edited by Daniel Marquard