Add customLogFiles sauce option

[ben-stevens-sauce]

Description

Add "customLogFiles" sauce:option, for uploading extra files at the end of a test.

Motivation and Context

At the end of a test, some mobile applications will write log files or crash reports to their own internal directory, which can be useful in debugging test failures. We should expose these files where appropriate to aid in problem identification.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation fix (typos, incorrect content, missing content, etc.)

Checklist

• [x] I have read the contributing document.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.