Add validation for "ServiceAccountNames" to avoid wrong taskname

[vincent-pli]

Fix issue #2582

Changes

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Release Notes

If define PipelineRun.Spec.ServiceAccountNames with a wrong TaskName (not existed in Pipeline definition), the PipelineRun will failed with InvalidServiceAccountMappings

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/pipelinerun/pipelinerun.go	72.3%	72.0%	-0.3
pkg/reconciler/pipelinerun/resources/pipelinerunresolution.go	90.2%	87.4%	-2.8

[afrittoli]

Thank you for this. Could you add unit test coverage?

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/reconciler/pipelinerun/pipelinerun.go	72.3%	72.0%	-0.3
pkg/reconciler/pipelinerun/resources/pipelinerunresolution.go	90.2%	90.1%	-0.1

[vincent-pli]

@afrittoli
UT added, thanks.

[afrittoli]

/kind bug

[afrittoli]

Thank you!
/approve

[vdemeester]

/lgtm

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: afrittoli, vdemeester

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