revert pruner keep and keep-since simultaneous support

[jkandasa]

Changes

tkn cli supports both "keep" and "keep-since", even though there is an issue with the logic
when we supply both "keep" and "keep-since", the outcome always equivalent to "keep", "keep-since" ignored
hence we strict with a single flag support until the issue is fixed in tkn cli
cli issue: tektoncd/cli#1990

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Release Notes

NONE

[jkandasa]

cc @rupalibehera @piyush-garg @vdemeester

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-operator-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/operator/v1alpha1/tektonconfig_validation.go	86.5%	84.6%	-1.9

[vdemeester]

/approve
/lgtn

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[jkandasa]

/cherry-pick main

[tekton-robot]

@jkandasa: new pull request created: #1505

In response to this:

/cherry-pick main

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[jkandasa]

/cherry-pick release-v0.66.x

[jkandasa]

/cherry-pick release-v0.67.x

[tekton-robot]

@jkandasa: new pull request created: #1506

In response to this:

/cherry-pick release-v0.66.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[tekton-robot]

@jkandasa: new pull request created: #1507

In response to this:

/cherry-pick release-v0.67.x

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.