Pipeline loop controller should set pipeline default spec to align with Tekton controller behavior

[Tomcli]

/kind feature

Description: [A clear and concise description of what your proposal. What problem does it solve?]

Additional information: [Miscellaneous information that will assist in solving the issue.]

[yhwang]

we can use the function here: https://github.com/tektoncd/pipeline/blob/main/pkg/apis/pipeline/v1beta1/pipeline_defaults.go#L33