Add support for exclude dir pattern

### What feature do you want to see added?

Add option to ignore dirs
```
junit testResults: '**/junit.xml', ignoreFolders: '**/node_modules'
```

I'm using pnpm that creates `node_modules` folder inside all packages in my monorepo folder.

### Upstream changes

_No response_

No source file or test is named; start by tracing how the junit testResults option is parsed and how result files are discovered in jenkinsci/junit-plugin. Add support for the proposed ignoreFolders pattern so nested node_modules directories can be excluded, then verify the behavior with the relevant existing tests or a focused test case.

Written by the indexing model from the issue text.