feat(browser-farm): Add Docker browser support for remote crawling

Implement initial MVP for Docker-based browser management in Crawl4ai, enabling
remote browser execution in containerized environments.

Key Changes:
- Add browser_farm module with Docker support components:
  * BrowserFarmService: Manages browser endpoints
  * DockerBrowser: Handles Docker browser communication
  * Basic health check implementation
  * Dockerfile with optimized Chrome/Playwright setup:
    - Based on python:3.10-slim for minimal size
    - Includes all required system dependencies
    - Auto-installs crawl4ai and sets up Playwright
    - Configures Chrome with remote debugging
    - Uses socat for port forwarding (9223)

- Update core components:
  * Rename use_managed_browser to use_remote_browser for clarity
  * Modify BrowserManager to support Docker mode
  * Add Docker configuration in BrowserConfig
  * Update context handling for remote browsers

- Add example:
  * hello_world_docker.py demonstrating Docker browser usage

Technical Details:
- Docker container exposes port 9223 (mapped to host:9333)
- Uses CDP (Chrome DevTools Protocol) for remote connection
- Maintains compatibility with existing managed browser features
- Simplified endpoint management for MVP phase
- Optimized Docker setup:
  * Minimal dependencies installation
  * Proper Chrome flags for containerized environment
  * Headless mode with GPU disabled
  * Security considerations (no-sandbox mode)

Testing:
- Extensive Docker configuration testing and optimization
- Verified with hello_world_docker.py example
- Confirmed remote browser connection and crawling functionality
- Tested basic health checks

This is the first step towards a scalable browser farm solution, setting up
the foundation for future enhancements like resource monitoring, multiple
browser instances, and container lifecycle management.

docs/examples/hello_world_docker.py

@@ -0,0 +1,31 @@
+import asyncio
+from crawl4ai import *
+
+async def main():
+    # Configure browser to use Docker
+    browser_config = BrowserConfig(
+        headless=True, 
+        verbose=True,
+        use_docker=True  # Enable Docker browser
+    )
+    
+    async with AsyncWebCrawler(config=browser_config) as crawler:
+        crawler_config = CrawlerRunConfig(
+            cache_mode=CacheMode.BYPASS,
+            markdown_generator=DefaultMarkdownGenerator(
+                content_filter=PruningContentFilter(
+                    threshold=0.48, 
+                    threshold_type="fixed",
+                    min_word_threshold=0
+                )
+            )
+        )
+        
+        result = await crawler.arun(
+            url="https://www.helloworld.org",
+            config=crawler_config
+        )
+        print(result.markdown_v2.raw_markdown[:500])
+
+if __name__ == "__main__":
+    asyncio.run(main())