tep: PipelineRun displayName

[say5]

Description

This pull request proposes the ability to define displayName for PipelineRun.
Based on TEP-0047: Pipeline Task Display Name representing the same idea but for the list of PipelineRun objects.

Good example of why it would be good to have it: tektoncd/dashboard#3323

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: say5 / name: Alexander Svyrydov (f2ef35e, 9acb882, e470519)

[tekton-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[vdemeester]

@say5 are you still interested to work on this TEP ? I can't see any content though, something might be wrong.