feat: add the ability to write log to file

[mato533]

Proposed changes

Add the ability to output logs to a file, mainly for the purpose of analyzing logs output to OutputChannel when the screen cannot be referenced, such as E2E testing in CI.

If a directory path is set in the environment variable VSCODE_WDIO_TRACE_LOG_PATH, a file vscode-webdriverio.log will be output to that directory, and all log messages will be output to that file.

This will contain all output regardless of the log level setting.

Types of changes

• Polish (an improvement for an existing feature)
• Bugfix (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 not work as expected)
• Documentation update (improvements to the project's docs)
• Internal updates (everything related to internal scripts, governance documentation and CI files)

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation (if appropriate)
• I have added proper type definitions for new commands (if appropriate)

Further comments

Reviewers: @webdriverio/project-committers