Update README.md with detailed release notes for Symfony MCP Server 1.4.0

- Introduce comprehensive overview of Sampling Support and its features.
- Add examples for Sampling Client integration and agentic tools (`CodeAnalyzerTool`, `ContentGeneratorTool`).
- Highlight key updates, including bug fixes, enhanced documentation, and real-world applications.
- Simplify README structure by removing verbose setup details and outdated sections.
- Provide resources for sampling documentation, example tools, and community discussions.
- Encourage adoption of newly added features with clear next steps.

Author: klapaudius