test_qoi_look_ahead.py: Create test, update tutorial

[swinter1]

Refines the handling of optimisation arguments in qoi_look_ahead.py.

• Clarifies the documentation of how optimization argument go from ModelBridge.gemn...) to the underlying 'scipy.optimize.minimize()` call by:
  • Improve docstring
  • improve code example
  • provide detailed trace
• Adds unit tests to ensure default get passed and are appropriately overridden.

Key files for review:

• tests/acquisition/test_qoi_look_ahead.py