Move generated JSON schema to /generated subfolder

- Updated generate_json_schema() to create JSON file in generated/ subfolder
- Added directory creation logic to ensure generated/ folder exists
- Removed old JSON file from root declarative/ directory
- Improves organization by clearly marking auto-generated files

Co-Authored-By: AJ Steers <aj@airbyte.io>

Author: devin-ai-integration[bot]