Build Tools: Allow easier customization of the .env file. #9826

Job	Run time
Core running from build / Core running from build / Linux	2m 5s
Core running from build / Core running from build / Windows	3m 56s
Core running from src / Core running from src / Linux	1m 50s
Core running from src / Core running from src / Windows	3m 32s
Core running from build / Core running from build / MacOS	2m 5s
Core running from src / Core running from src / MacOS	2m 24s
Gutenberg running from build / Gutenberg running from build / Linux	8m 5s
Gutenberg running from src / Gutenberg running from src / Linux	8m 4s
Gutenberg running from build / Gutenberg running from build / Windows	12m 6s
Gutenberg running from src / Gutenberg running from src / Windows	11m 34s
Gutenberg running from build / Gutenberg running from build / MacOS	7m 44s
Gutenberg running from src / Gutenberg running from src / MacOS	7m 48s
Slack Notifications / Prepare notifications	3s
Slack Notifications / Success notifications	3s
Slack Notifications / Failure notifications	0s
Slack Notifications / Fixed notifications	0s
Slack Notifications / Cancelled notifications	0s
Failed workflow tasks	0s
	1h 11m 19s

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