feat: integrate relation extraction

- Updated webservice call to use `/extract_entities_relations` endpoint
with `with_relations=true` param.
- Extended parsing logic to handle `relationships` from ML model
response.
- Tracked text-to-STIX ID mapping for relationship linking.
- Added support for Identity types (Sector, Organization, Individual)
and custom object Channel.
- Created STIX relationships dynamically from predicted data when valid
source/target IDs are found.
- Preserved original fallback logic for known relationship rules.

Author: SoniaBadene