Fix incorrect reference to Remote Custom ruleset file

What does this MR do?

Problem: When loading a remote Secrets Detection ruleset file, the current logic looks for .gitlab/sast-ruleset.toml file instead of .gitlab/secret-detection-ruleset.toml in the remote repository. This results in ignoring the remote custom ruleset file. More info on the issue is outlined here.

Fix: New logic looks for the appropriate file based on the analyzer in context.

What are the relevant issue numbers?

https://gitlab.com/gitlab-com/sec-sub-department/section-sec-request-for-help/-/issues/83

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests updated/added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer