docs: improve graphql documentation #6814

Job	Run time
lint (18.x)	4m 1s
test-formio (18.x)	3m 5s
test-graphql (18.x)	4m 51s
test-core (18.x)	4m 16s
test-orm (18.x)	4m 3s
test-platform (18.x)	3m 10s
test-security (18.x)	4m 9s
test-integration (ubuntu-latest, 16.x)	4m 47s
test-integration (ubuntu-latest, 18.x)	4m 24s
test-integration (ubuntu-latest, 19.x)	3m 5s
test-third-parties (18.x)	3m 1s
test-integration (macos-latest, 18.x)	7m 36s
test-specs (18.x)	3m 23s
test-integration (windows-latest, 18.x)	14m 47s
deploy-packages	0s
publish-docs	0s
	1h 8m 38s

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