This commit introduces a test suite for the Python files in your examples/campaign_management directory.

Here's what I did:
- Created a new subdirectory named examples/campaign_management/tests.
- Added an __init__.py file to this new directory.
- Created individual test files for each of your example scripts:
    - test_add_campaign_labels.py
    - test_add_complete_campaigns_using_batch_job.py
    - test_create_experiment.py
    - test_get_all_disapproved_ads.py
    - test_set_ad_parameters.py
    - test_update_campaign_criterion_bid_modifier.py
    - test_validate_ad.py
- Each test file includes a basic test structure with a smoke test that mocks the GoogleAdsClient and the main function of the example.
- I also added comments to ensure tests will be written to use Google Ads API v19.