Update links to demos in Pipeline SD docs

What does this MR do and why?

This merge request updates Pipeline Secret Detection documentation to link to the demo projects I created today:

• Ignore paths with Gitleaks’ native [allowlist] functionality:
  • Using a local ruleset via file passthrough.
  • Using a remote ruleset via git passthrough.
  • Using a remote ruleset via url passthrough.
• Ignore patterns with Gitleaks’ native [allowlist] functionality:
  • Using a local ruleset via file passthrough.
  • Using a remote ruleset via git passthrough.
  • Using a remote ruleset via url passthrough.
• Ignore values with Gitleaks’ native [allowlist] functionality:
  • Using a local ruleset via file passthrough.
  • Using a remote ruleset via git passthrough.
  • Using a remote ruleset via url passthrough.

MR acceptance checklist

I have evaluated this MR against the MR acceptance checklist.