feat: Add --data-path CLI flag for persistent data separation (#8888)

feat: add --data-path CLI flag for persistent data separation

- Add LOCALAI_DATA_PATH environment variable and --data-path CLI flag
- Default data path: /data (separate from configuration directory)
- Automatic migration on startup: moves agent_tasks.json, agent_jobs.json, collections/, and assets/ from old config dir to new data path
- Backward compatible: preserves old behavior if LOCALAI_DATA_PATH is not set
- Agent state and job directories now use DataPath with proper fallback chain
- Update documentation with new flag and docker-compose example

This separates mutable persistent data (collectiondb, agents, assets, skills) from configuration files, enabling better volume mounting and data persistence in containerized deployments.

Signed-off-by: localai-bot <localai-bot@noreply.github.com>
Co-authored-by: localai-bot <localai-bot@noreply.github.com>