docs: improve graphql documentation #6810

Job	Run time
lint (18.x)	4m 38s
test-integration (ubuntu-latest, 16.x)	3m 59s
test-core (18.x)	3m 25s
test-integration (ubuntu-latest, 18.x)	4m 52s
test-integration (ubuntu-latest, 19.x)	4m 14s
test-integration (macos-latest, 18.x)	5m 42s
test-specs (18.x)	3m 18s
test-integration (windows-latest, 18.x)	14m 17s
test-graphql (18.x)	4m 22s
test-orm (18.x)	3m 25s
test-platform (18.x)	4m 26s
test-formio (18.x)	2m 22s
test-third-parties (18.x)	3m 33s
test-security (18.x)	2m 59s
deploy-packages	0s
publish-docs	0s
	1h 5m 32s

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