Backport to 17.9 the fix to support custom pipcompile requirement file with the new DS analyzer

What does this MR do and why?

Backport to 17.9 for the fix Support custom pipcompile lockfile in DS latest... (!182159 - merged)

This bug could affect some self-managed customers upgrading to 17.9 and willing to start their transition to the new DS analyzer.

Describe in detail what merge request is being backported and why

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has either succeeded or been approved by a Software Engineer in Test.

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• Refer to the patch release runbook for engineers and maintainers for guidance.
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