Docs (envvars): Improve documentation on available environment variables #126

Job	Run time
test-powershell-5-1-windows-2022	1m 17s
test-powershell-5-1-windows-2019	1m 22s
test-powershell-6-2-container	15s
test-powershell-6-1-container	16s
test-powershell-7-0-container	14s
test-powershell-7-1-container	15s
test-powershell-core-linux	26s
test-powershell-core-macos	17s
test-powershell-core-windows	58s
test-powershell-7-2-container	12s
test-powershell-7-3-container	13s
test-powershell-7-4-container	13s
	5m 58s

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