test check_custom_event resource

[davidbloss]

Resolves # Add missing Terraform integration tests for opslevel_check_custom_event

⚠️ WIP: waiting on upstream feature

Problem

Solution

Checklist

• I have run this code, and it appears to resolve the stated issue.
• This PR does not reduce total test coverage
• This PR has no user interface changes or has already received approval from product management to change the interface.
• Make a changie entry that explains the customer facing outcome of this change