Support comma-separated glob patterns for test reports

What does this MR do and why?

Describe in detail what your merge request does and why.

Introduces ability for Artifacts class to support comma-separated glob patterns for the test_reports parameter (e.g. "jest/**/*.json,rspec/**/*.json").

This is needed for consolidated CI jobs that need to process test reports from multiple sources in a single invocation.

Related: gitlab-org/quality/analytics/team#339

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