v1.15.1: burr dependency not optional

[LorenzoPaleari]

Describe the bug Burr package is required in order to start any example of ScrapeGraphAI.

To Reproduce

pip install scrapegraphai
playwright install
python3 smart_scraper_openai.py # examples/openai/smart_scraper_openai.py

Expected behaviour Burr should be installed only if used.

(venv) lollo@Lorenzos-MacBook-Pro test % python3 smart_scraper_openai.py 
Traceback (most recent call last):
  File "/Users/lollo/Desktop/test/venv/lib/python3.11/site-packages/scrapegraphai/integrations/burr_bridge.py", line 13, in <module>
    import burr
ModuleNotFoundError: No module named 'burr'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/lollo/Desktop/test/smart_scraper_openai.py", line 8, in <module>
    from scrapegraphai.graphs import SmartScraperGraph
  File "/Users/lollo/Desktop/test/venv/lib/python3.11/site-packages/scrapegraphai/graphs/__init__.py", line 6, in <module>
    from .base_graph import BaseGraph
  File "/Users/lollo/Desktop/test/venv/lib/python3.11/site-packages/scrapegraphai/graphs/base_graph.py", line 8, in <module>
    from ..integrations import BurrBridge
  File "/Users/lollo/Desktop/test/venv/lib/python3.11/site-packages/scrapegraphai/integrations/__init__.py", line 5, in <module>
    from .burr_bridge import BurrBridge
  File "/Users/lollo/Desktop/test/venv/lib/python3.11/site-packages/scrapegraphai/integrations/burr_bridge.py", line 18, in <module>
    raise ImportError("burr package is not installed. Please install it with 'pip install scrapegraphai[burr]'")
ImportError: burr package is not installed. Please install it with 'pip install scrapegraphai[burr]'

Desktop (please complete the following information):

• OS: MacOsX - MacBookPro 2018
• Version: python3.11