feat: Optimize performance with background polling and add project filtering via tags

[1azunna]

• Implemented background polling: Added an internal cache and background worker to refresh metrics asynchronously, preventing scrape timeouts and reducing load on the Dependency-Track API.
• Added tag-based project filtering: New --dtrack.project-tags flag to export metrics only for projects matching specific tags.
• Refactored metrics collection to use a push-based registry model, significantly improving performance in environments with many projects.