Add limit to number of test cases parsed

What does this MR do?

Solves #247886 (closed)

Related discussion: #247886 (comment 418666939)

Adds a hardcoded limit that only applies to .com. This is for the max number of test cases allowed to be parsed by the JUnit parser. If the limit is exceeded, an error message will be displayed on the MR widget.

Unfortunately, we can't rely on test_suite.total_count as basis for test cases parsed because it counts test cases uniquely by their key(classname + name). So if there's a malicious file that contains just a bunch of duplicate test cases, we won't be able to catch it.

Screenshots

Does this MR meet the acceptance criteria?

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