add `mariadb.global.defaultStorageClass` to values.yaml #1081

Job	Run time
changes	6s
lint	35s
test (Default - no custom values)	1m 46s
test (PostgreSQL Enabled, --helm-extra-set-args "--set=postgresql.enabled=true --set=postgresql.g...	2m 10s
test (Nginx Enabled, --helm-extra-set-args "--set=image.flavor=fpm --set=nginx.enabled=true")	1m 38s
test (Horizontal Pod Autoscaling Enabled, --helm-extra-set-args "--set=hpa.enabled=true --set=hpa...	1m 50s
test (S3 Enabled as Primary Storage, --namespace nextcloud --skip-clean-up --helm-extra-set-args ...	1m 46s
summary	4s
	9m 55s

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