Provide examples for pathfilter

What does this MR do?

• Provide examples for the pathfilter package
• Fix rendering problems in documentation of Match
• Add package overview

This can be tested locally using godoc.

What are the relevant issue numbers?

None.

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 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