Add namespace variable interpolation for pipelinerun namespace and

[R2wenD2]

taskrun namespace

Changes

Add namespace variable interpolation for pipelinerun namespace and taskrun namespace this will be the final diff for #1522

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Release Notes

[R2wenD2]

/kind feature

[ghost]

some questions on the tests but the change itself lgtm

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[R2wenD2]

Thanks for the review, good catches - just a few copy/paste errors in the taskrun test.

[dibyom]

/lgtm