Add `getOptionalEnvVar` helper #1819

Job	Run time
Upload debug artifacts after failure in analyze (stable-v2.20.3)	1m 55s
Upload debug artifacts after failure in analyze (linked)	3m 53s
Upload debug artifacts after failure in analyze (default)	3m 18s
Upload debug artifacts after failure in analyze (nightly-latest)	3m 15s
Download and check debug artifacts after failure in analyze	16s
	12m 37s

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