Add support for double star glob patterns

What does this MR do?

Adds support for double star glob patterns. The original behaviour of pathfilter.Match is retained for patterns that don't include globstars (**).

What are the relevant issue numbers?

• gitlab-org/gitlab#224440 (closed)

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
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• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer