[test] allow env variable for opencti configuration in tests (#981)

[aHenryJard]

Proposed changes

• Add environement variable (same as the one in example folder)
• Default to previous values

Needed for OpenCTI-Platform/opencti#12446

Related issues

• closes Make opencti URL and token configurable via env var for examples and tests #981

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

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...