issue with keep and keep-since in taskrun and in pipelinerun

[jkandasa]

tkn version: 0.30.1

keep and keep-since support is introduced in https://github.com/tektoncd/cli/pull/1533 though, when we supply keep and keep-since simultaneously the out come always equivalent to keep, keep-since ignored

Pipelinerun: https://github.com/tektoncd/cli/blob/f4d092c77d359a48dfdecf708f72293ebf872f5a/pkg/cmd/pipelinerun/delete.go#L329-L338

taskrun: https://github.com/tektoncd/cli/blob/f4d092c77d359a48dfdecf708f72293ebf872f5a/pkg/cmd/taskrun/delete.go#L379-L388

Expected behavior

• tkn taskrun delete --keep=5 --keep-since=30
• after executed the above command, remaining taskruns will be as count <= 5 and start-time <= 30 minutes
• this is applicable for pipelineruns too

[pratap0007]

/assign

[jkandasa]

@pratap0007 have you started working on this issue? if not shall I take this one?