Clarify pipeline's execution step and execution status

The enum values at https://github.com/AdobeDocs/cloudmanager-api-docs/blob/232bfdf117055fc2d9843b3fd970cdc50f2cf83e/swagger-specs/api.yaml#L1616 and https://github.com/AdobeDocs/cloudmanager-api-docs/blob/232bfdf117055fc2d9843b3fd970cdc50f2cf83e/swagger-specs/api.yaml#L1707 should be clarified with respect to differences between `error` and `failure`.

I assume that `failure` means the build failed due to some constraint violation while `error` is a transient error in the backend (so retries may work), but this is just my guess.