[Google TI Feeds] fetch relationship entities directly from collections API

[jabesq]

Proposed changes

• Refactored relationship retrieval to use direct collections endpoints (/collections/{entity_id}/{entity_type}) and return related entities directly instead of re-fetching details, reducing extra API calls and simplifying data flow.
• Updated orchestrators (campaign, malware, report, threat_actor, vulnerability) to consume direct related-entity payloads while preserving attack-technique ID-only optimization.
• Updated fixtures and assertions in orchestrator/config tests to match direct relationship payload behavior and improve stability.
• Updated CONTRIBUTING.md to reference the renamed API method (fetch_subentities).
• Added a follow-up style commit normalizing test file line endings to satisfy black in pre-commit.

Related issues

• Closes [Google TI] Reduce quota usage by resolving related entities #6236

Checklist

• I consider the submitted work as finished
• I have signed my commits using GPG key.
• I tested the code for its functionality using different use cases
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Comments

Prometheus metrics (from PR #6307),

Before changes:

# HELP google_ti_feeds_api_endpoint_calls_total Count of API calls made by GenericFetcher for each Google TI Feeds API endpoint
# TYPE google_ti_feeds_api_endpoint_calls_total counter
google_ti_feeds_api_endpoint_calls_total{endpoint="/collections"} 1.0
google_ti_feeds_api_endpoint_calls_total{endpoint="/collections/{entity_id}/relationships/{entity_type}"} 74.0
google_ti_feeds_api_endpoint_calls_total{endpoint="/collections/{entity_id}"} 112.0
google_ti_feeds_api_endpoint_calls_total{endpoint="/files/{entity_id}"} 22.0
google_ti_feeds_api_endpoint_calls_total{endpoint="/urls/{entity_id}"} 21.0

After:

python_info{implementation="CPython",major="3",minor="12",patchlevel="12",version="3.12.12"} 1.0
# HELP google_ti_feeds_api_endpoint_calls_total Count of API calls made by GenericFetcher for each Google TI Feeds API endpoint
# TYPE google_ti_feeds_api_endpoint_calls_total counter
google_ti_feeds_api_endpoint_calls_total{endpoint="/collections"} 1.0
google_ti_feeds_api_endpoint_calls_total{endpoint="/collections/{entity_id}/{entity_type}"} 74.0

[codecov]

Codecov Report

❌ Patch coverage is 83.14607% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 14.33%. Comparing base (1504ad6) to head (63d22e5).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...nnector/src/custom/client_api/client_api_shared.py	68.75%	10 Missing ⚠️
.../google-ti-feeds/tests/custom/test_orchestrator.py	63.63%	4 Missing ⚠️
...-feeds/tests/octi/configs/test_connector_config.py	95.83%	1 Missing ⚠️

❗ There is a different number of reports uploaded between BASE (1504ad6) and HEAD (63d22e5). Click for more details.

HEAD has 93 uploads less than BASE

Flag	BASE (1504ad6)	HEAD (63d22e5)
connectors	95	2

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #6316       +/-   ##
===========================================
- Coverage   40.60%   14.33%   -26.28%     
===========================================
  Files        2142     1705      -437     
  Lines      128325   108573    -19752     
===========================================
- Hits        52102    15560    -36542     
- Misses      76223    93013    +16790     

Flag	Coverage Δ
baseline	0.00% <0.00%> (ø)
connectors	92.56% <83.14%> (+18.37%)	⬆️

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[romain-filigran]

Note: I would like to functionally validate this PR before merging it

[romain-filigran]

All good for me. Thank you @jabesq