Update JobEvent webhook type to reflect GitLab documentation

Added following tags which were missing from the API model:

• build_created_at_iso
• build_started_at_iso
• build_finished_at_iso
• project

Note: While GitLab webhook events documentation shows the ci_config_path in the project object as nullable, in my testing (on a self-hosted instance) I noticed that it was an empty string; hence the difference in the test data payload.

See relevant part of the GitLab documentation here.