Find or initialize instance-level integration
What does this MR do?
!26454 (merged) implemented the basic feature under a feature flag, this implements the backend changes.
This is similar to the service templates feature that we are going to remove &2430. As for service templates, we are not using the testing settings functionality because is coupled to a project that we don't have in this context.
We will enable the testing settings functionality one-by-one #213138.
Related to: #208914 (closed) #199388 (closed)