feat: Add pipeline timings and toggle visualization, establish debug settings

[cau-git]

This PR introduces two new features:

1. Time profiling of the pipelines . The ConversionResult object carries a new field timings, which will be populated if the respective setting settings.debug.profile_pipeline_timings is turned on. The measurements are distinguished by scope (Page or Document) and the profiled sections, which rely on the newly implemented TimeRecorder context manager.
2. Debug visualisations. We have new settings fields to control whether the cells, ocr, layout or table structure predictions should be visualized. When they are turned on, debug visualisations will be saved as PNG iamges by default under {current_working_directory}/debug/.

Checklist:

• Commit Message Formatting: Commit titles and messages follow guidelines in the
  conventional commits.
• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

[PeterStaar-IBM]

lgtm