fix(backend): add PR name substitution for scheduled runs.

[HumairAK]

Which issue is resolved by this Pull Request:
Resolves #1343

Description of your changes:
The change ensures instanes of ORIG_PR_NAME are properly substituted for scheduled runs, just like in manually triggered runs. It also adds the missing custom.tekton.dev/originalPipelineRun. Both cases are handled in SWF controller, since workflow names for recurring runs are generated there.

Environment tested:

• Python Version (use python --version):
• Tekton Version (use tkn version):
• Kubernetes Version (use kubectl version):
• OS (e.g. from /etc/os-release):

Checklist:

• The title for your pull request (PR) should follow our title convention. Learn more about the pull request title convention used in this repository.

[Tomcli]

thanks @HumairAK

/lgtm
/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: HumairAK, Tomcli

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