[SUREFIRE-1834] Make warnings for skipped tests configurable

**[Martin Winandy](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=pmwmedia)** opened **[SUREFIRE-1834](https://issues.apache.org/jira/browse/SUREFIRE-1834?redirect=false)** and commented

Currently, Surefire outputs warnings for skipped tests.

For example:

```
[WARNING] Tests run: 4, Failures: 0, Errors: 0, Skipped: 2, Time elapsed: 0.037 s - in org.tinylog.core.runtime.LegacyStackTraceAccessTest
[WARNING] Tests run: 62, Failures: 0, Errors: 0, Skipped: 2
```

I have some platform depending tests, which are enabled or disabled depending on the actual platform. It would be great, if a property could be introduced to disable warnings for skipped tests.

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**Affects:** 3.0.0-M5

No source files or tests are named in the issue. Start by tracing where Surefire formats warnings for skipped tests and how plugin properties are declared; done means a documented configuration property suppresses those warnings while preserving skipped-test counts.

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