Allow from_or_to_id to get relationship

[DucNg]

Proposed changes

• Allow read relationship using from_or_to_id

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

I guess it's a programming oversight not to allow read using from_or_to_id since it works just by adding this condition.
I'm open to adding a test case for this change but I wasn't able to find a proper example with fixtures.

How to test

• Get the id of an element with a relationship from your OpenCTI

import pycti

OPENCTI_URL = "http://localhost:8080"
OPENCTI_TOKEN = "<token>"
opencti_client = pycti.OpenCTIApiClient(OPENCTI_URL, OPENCTI_TOKEN)
toto = opencti_client.stix_core_relationship.read(
    fromOrToId="<id of an element with a relationship>"
)
print(toto)

[DucNg]

Should be done using list(): https://filigran-community.slack.com/archives/C06CC3T5Z37/p1727687428380199