Update Security Configuration page to link to SAST Configuration UI

What does this MR do?

Add links to SAST Configuration UI

This modifies the Security Configuration page for a project to display a link to the SAST Configuration UI for eligible projects. Roughly speaking, that means projects without an existing CI file. Future iterations will expand the scope of eligible projects.

This is implemented behind the sast_configuration_ui feature flag, which will be removed or enabled by default in #231357 (closed).

Addresses #231373 (closed).

Screenshots

State	Screenshot with feature flag disabled	Screenshot with feature flag enabled
Existing CI file (i.e., no change)
No CI file
No CI file with Auto DevOps (i.e., no visible change (button becomes a link button to SAST Configuration UI page))

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

• 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