Extend JUnit XML test report documentation to explicitly mention support for filename patterns.

What does this MR do?

Amend the recently introduced Documentation for JUnit XML test summary in MRs to explicitly mention that the value junit can also be a filename pattern.

This information was mentioned only in the accompanying article "JUnit test reports" until now.

Additionally, add a more explicit link to "JUnit test reports" (there was already one, but it was not mentioned with the context of providing additional examples).

Related issues

Related: #45318 (closed)

Author's checklist

• Apply the correct labels and milestone
• Crosslink the document from the higher-level index
• Crosslink the document from other subject-related docs
• Correctly apply the product badges and tiers
• Port the MR to EE (or backport from CE): always recommended, required when the ee-compat-check job fails

Review checklist

• Your team's review (required)
• PM's review (recommended, but not a blocker)
• Technical writer's review (required)
• Merge the EE-MR first, CE-MR afterwards