fix(gatsby): always add both childField and childrenField in Grap…

…hQL (gatsbyjs#28656)

* fix(gatsby): always add both `childField` and `childrenField` in GraphQL

* Update docs

* fix null reference

* Update tests

* TODO item to remove `many` arg in `v3`

* Update snapshot

* add description to convenience child fields

* update description

* Revert docs for now

yarn.lock

@@ -1761,12 +1761,7 @@
     "@types/node" "*"
     form-data "^3.0.0"
 
-"@types/node@*":
-  version "14.14.7"
-  resolved "https://registry.yarnpkg.com/@types/node/-/node-14.14.7.tgz#8ea1e8f8eae2430cf440564b98c6dfce1ec5945d"
-  integrity sha512-Zw1vhUSQZYw+7u5dAwNbIA9TuTotpzY/OF7sJM9FqPOF3SPjKnxrjoTktXDZgUjybf4cWVBP7O8wvKdSaGHweg==
-
-"@types/node@^8.5.7":
+"@types/node@*", "@types/node@^8.5.7":
   version "8.10.66"
   resolved "https://registry.yarnpkg.com/@types/node/-/node-8.10.66.tgz#dd035d409df322acc83dff62a602f12a5783bbb3"
   integrity sha512-tktOkFUA4kXx2hhhrB8bIFb5TbwzS4uOhKEmwiD+NoiL0qtP2OQ9mFldbgD4dV1djrlBYP6eBuQZiWjuHUpqFw==