Pin major version of SAST analyzers

What does this MR do?

As a follow-up to the recently released DinD-free version of SAST, for the non-Docker-in-Docker analyzers, we have pinned the major version to 2. This can be overriden with the SAST_MAJOR_VERSION environment variable.

Also, the non-Docker-in-Docker analyzers now utilize the SAST_DEFAULT_ANALYZERS environment variable.

And in order to address this bug #32412 (closed), we are no longer inheriting from .sast at all. The non-Docker-in-Docker analyzers now inherit from sast.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

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