chore: streamline README/config docs and add permissions to CI #1162

Job	Run time
check-flavor	9s
validate (install, unicorn) / run	41s
validate (upgrade, registry1) / run	39s
validate (install, upstream) / run	40s
validate (install, registry1) / run	41s
validate (upgrade, unicorn) / run	39s
validate (upgrade, upstream) / run	30s
	3m 59s

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