Fix logic in Event Notifications DA which prevents creating service specific credentials using secrets manager

[ocofaigh]

Since the Event Notifications DA supports creating service specific roles, it is impacted by the same bug reported here: terraform-ibm-modules/terraform-ibm-cos#817

After step 1 and 2 here are implemented we need to update the logic in Event Notifications DA as per step 3. Fix should be consistent with the code change done in COS DA.

[shemau]

This is resolved by #374 in 1.17.0