docs: improve graphql documentation #6808

Job	Run time
lint (18.x)	4m 3s
test-graphql (18.x)	3m 9s
test-formio (18.x)	3m 31s
test-core (18.x)	3m 8s
test-integration (ubuntu-latest, 16.x)	5m 17s
test-orm (18.x)	3m 55s
test-platform (18.x)	3m 21s
test-integration (ubuntu-latest, 18.x)	3m 6s
test-security (18.x)	3m 45s
test-integration (ubuntu-latest, 19.x)	3m 3s
test-integration (macos-latest, 18.x)	6m 17s
test-integration (windows-latest, 18.x)	15m 24s
test-third-parties (18.x)	2m 58s
test-specs (18.x)	3m 21s
deploy-packages	0s
publish-docs	0s
	1h 4m 18s

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