Add new dep scanning var for python requirements

What does this MR do?

This MR adds a new variable for the dependency scanning template. This variable allows users to specify the pip requirements file that the python analyzer should use.

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

Closes #8524 (closed)