Drop DinD for SAST, DS

What does this MR do?

Drop Docker-in-Docker (DinD) mode for SAST and Dependency Scanning:

• remove the variable used to enable the DinD mode
• change sast and dependency_scanning jobs
  • update the rules so that they're not triggered
  • update the script so that they fail with an explicit error message
  • remove the allow_failure attribute, making sure they do fail when triggered

As a result, it's not possible to change the default value of allow_failure using sast or dependency_scanning. The benefit is that users will be forced to notice the misuse of these jobs.

See #220540 (closed)

Tested with tests/go-modules

• in non-DinD setup, scanning jobs and QA jobs are triggered: https://gitlab.com/gitlab-org/security-products/tests/go-modules/-/pipelines/185126593
• in DinD setup, no-DinD scanning jobs are triggered: https://gitlab.com/gitlab-org/security-products/tests/go-modules/-/pipelines/185125415
• in DinD setup, sast and dependency_scanning fail with an error message when enabled: https://gitlab.com/gitlab-org/security-products/tests/go-modules/-/pipelines/185137829

Also, tested with apex-salesforce to make sure that the sast job can be overridden. This pipeline fails as expected: https://gitlab.com/gitlab-org/security-products/tests/apex-salesforce/-/pipelines/185136220

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation Documentation is updated in a separate MR.
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team