test: use Pester instead of self-rolled util scripts (#81) #189

Job	Run time
cli-integration (ubuntu)	9s
cli-integration (macos)	12s
cli-integration (windows)	23s
updater-create-pr / cancel-previous-run	2s
updater-test-args / cancel-previous-run	3s
updater-create-pr / update	14s
updater-test-args / update	12s
updater-test-outputs	1s
	1m 16s

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