STIX & TAXII Export Enhancements

[AlyaGomaa]

1. STIX Export Enhancements

• Added threat_level to meta in StixExporter for richer evidence descriptions.
• Included observed and created timestamps in STIX metadata for better temporal context.
• Improved STIX indicator descriptions with metadata and valid time information.
• Refactored STIX XML formatting for readability and correctness.
• Enhanced STIX export logic to support direct export and improve error messaging.
• Enhanced logging for STIX export: included sample objects and detailed error messages.
• Added error handling and IP validation in STIX export.

2. TAXII Integration Updates

• Added TAXII version support and configuration retrieval methods.
• Updated TAXII content binding to use attribute format.
• Corrected TAXII inbox XML structure and consolidated collection names.
• Enhanced direct export functionality for TAXII alerts, including configuration for workers, retries, backoff delays, and caching.
• Added taxii_timeout parameter for HTTP requests and updated direct_export_retry_max to allow infinite retries.

3. Direct Export Worker Implementation

• Implemented direct export workers for STIX evidence with graceful shutdown.
• Introduced worker configuration and evidence locking to manage concurrent exports safely.
• Refactored worker management and error handling for robustness.

4. Configuration and Documentation

• Updated slips.yaml documentation for TAXII_server parameter.
• Added configuration options for direct export retry, worker management, and backoff delays.

5. Miscellaneous

• Implemented SQLite queue for direct export of evidence to improve reliability.
• Added handling for None in data_to_send in ScanDetectionsHandler.
• Added old-pipeline directory to .gitignore.