feat(content): add target_elements parameter for selective content extraction

Adds new target_elements parameter to CrawlerRunConfig that allows more flexible content selection than css_selector. This enables focusing markdown generation and data extraction on specific elements while still processing the entire page for links and media.

Key changes:
- Added target_elements list parameter to CrawlerRunConfig
- Modified WebScrapingStrategy and LXMLWebScrapingStrategy to handle target_elements
- Updated documentation with examples and comparison between css_selector and target_elements
- Fixed table extraction in content_scraping_strategy.py

BREAKING CHANGE: Table extraction logic has been modified to better handle thead/tbody structures

deploy/docker/README.md

@@ -352,7 +352,10 @@ Example:
 from crawl4ai import CrawlerRunConfig, PruningContentFilter
 
 config = CrawlerRunConfig(
-    content_filter=PruningContentFilter(threshold=0.48)
+    markdown_generator=DefaultMarkdownGenerator(
+        content_filter=PruningContentFilter(threshold=0.48, threshold_type="fixed")
+    ),
+    cache_mode= CacheMode.BYPASS
 )
 print(config.dump())  # Use this JSON in your API calls
 ```