Add EventQuery to symbols exported from query.py by events/__init__.py

[taldcroft]

Description

ska_testr integration showed a script that was expecting EventQuery to be available as an import from kadi.events, so this adds that in.

Interface impacts

Fixes an unexpected API change where EventQuery was not available.

Testing

Unit tests

• [x] Mac

Functional tests

With PYTHONPATH set to the git repo at this branch, I ran run_testr --include kadi:

• Without the fix (current master) I reproduced the failure related to EventQuery seen in ska3-flight 2022.7rc2.
• With the fix all tests pass.