Update upgrade notes in `CONTRIBUTING.md`, `README.md`, `values.yaml` #1058

Job	Run time
changes	10s
lint	1m 7s
run-tests (Default - no custom values)	1m 49s
run-tests (PostgreSQL Enabled, --helm-extra-set-args "--set=postgresql.enabled=true --set=postgre...	2m 12s
run-tests (Nginx Enabled, --helm-extra-set-args "--set=image.flavor=fpm --set=nginx.enabled=true")	1m 42s
run-tests (Horizontal Pod Autoscaling Enabled, --helm-extra-set-args "--set=hpa.enabled=true --se...	1m 51s
summary	5s
	8m 56s

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