feat: Implementation of HTML backend with headless browser (#2969)

- Implementation of HTML backend that (optionally) uses headless browser (via Playwright) to materialize HTML pages into images, and add provenances with bboxes to all elements in the converted docling document.
- Conversion preserves reading order given by HTML DOM tree
- Added support for HTML "input" fields: checkboxes, radiobuttons, text inputs, etc.
- Added support to Key-Value convention in HTML (i.e. elements with id "key1" and "key1_value1" will be paired as key-values, see test cases as examples)
- Heuristic that glues independent inline HTML elements with single-character text in them into larger text blocks
- Support for inline styling (bold, italic, etc.)

Signed-off-by: Maksym Lysak <mly@zurich.ibm.com>
Co-authored-by: Maksym Lysak <mly@zurich.ibm.com>

Author: maxmnemonic

.github/workflows/checks.yml

@@ -20,7 +20,7 @@ env:
     tests/test_asr_pipeline.py
     tests/test_threaded_pipeline.py
   PYTEST_TO_SKIP: |-
-  EXAMPLES_TO_SKIP: '^(batch_convert|compare_vlm_models|minimal|minimal_vlm_pipeline|minimal_asr_pipeline|export_multimodal|custom_convert|develop_picture_enrichment|rapidocr_with_custom_models|suryaocr_with_custom_models|offline_convert|pictures_description|pictures_description_api|vlm_pipeline_api_model|granitedocling_repetition_stopping|mlx_whisper_example|gpu_standard_pipeline|gpu_vlm_pipeline|demo_layout_vlm|post_process_ocr_with_vlm)\.py$|xbrl_conversion\.ipynb$'
+  EXAMPLES_TO_SKIP: '^(batch_convert|compare_vlm_models|minimal|minimal_vlm_pipeline|minimal_asr_pipeline|export_multimodal|custom_convert|develop_picture_enrichment|rapidocr_with_custom_models|suryaocr_with_custom_models|offline_convert|pictures_description|pictures_description_api|vlm_pipeline_api_model|granitedocling_repetition_stopping|mlx_whisper_example|gpu_standard_pipeline|gpu_vlm_pipeline|demo_layout_vlm|post_process_ocr_with_vlm|run_with_formats_html_rendered|run_with_formats_html_rendered_mp)\.py$|xbrl_conversion\.ipynb$'
 
 jobs:
   lint: