Add spec for task_completion_status
Add test cases for task_completion_status result
Extracted shared samples
Add new spec file for task completion status response
Fix style errors
Add changelog entry
Changed samples to Hashes
Remove test for successful request
Remove not nil expectation
Add task_completion_status to api documentation for issues
Add task_completion_status to api documentation for merge_requests
Refactor spec so it just requests one specific item
Add task_completion_status to Taskable
Simplified task completion status in entities
Refactor spec so it separates status code check and content check
Fix spec description text and field name
