GraphQL: Handle required fields from Parse Schema

[Moumouls]

A little improvement for better front DX

[Moumouls]

Seems we have a Postgres extension fail

[codecov]

Codecov Report

Merging #6271 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #6271      +/-   ##
=========================================
- Coverage   93.85%   93.8%   -0.05%     
=========================================
  Files         169     169              
  Lines       11564   11564              
=========================================
- Hits        10853   10848       -5     
- Misses        711     716       +5

Impacted Files	Coverage Δ
src/GraphQL/loaders/parseClassTypes.js	94.23% <ø> (ø)	⬆️
src/Adapters/Storage/Mongo/MongoStorageAdapter.js	92.74% <0%> (-0.71%)	⬇️
src/RestWrite.js	93.58% <0%> (-0.33%)	⬇️

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[Moumouls]

Build Fail for 1 test suite: https://travis-ci.org/parse-community/parse-server/builds/622692292?utm_medium=notification&utm_source=github_status

[dplewis]

@Moumouls I'll fix it in another PR. You should be good for now.

[Moumouls]

I'll push again on this branch, i missed to add required field on output fields...

[davimacedo]

Maybe it would be better to send a new pr with the output.