Adding utility to mock environment variables

[eyalkoren]

Adding a utility to test scenarios with custom env variables.
Originally implemented for removal of system-lambda (as part of #2184), but I want to use it in a current PR I am doing now.

[apmmachine]

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• Start Time: 2021-10-18T08:29:14.478+0000

• Duration: 59 min 45 sec

• Commit: cee4bf3

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Test	Results
Failed	0
Passed	2427
Skipped	19
Total	2446

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[eyalkoren]

closes #1942