Fix Apollo subscription message handling

[smyrick]

📝 Description

Support the messages that come from the Apollo client subscriptions.

https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md

We need to wrap the GraphQLRequest and GraphQLResponse in a special message before we send it over the web socket. That message structure is implemented in the handler for the graphql-ws protocol

🔗 Related Issues

Fixes #370

[smyrick]

Two examples of sending the Keep alive message

https://github.com/leangen/graphql-spqr-spring-boot-starter/blob/0f5d66d478233d3d8401c1e5e4736ac3ed59d793/graphql-spqr-spring-boot-autoconfigure/src/main/java/io/leangen/graphql/spqr/spring/web/apollo/ApolloProtocolHandler.java#L51

and

https://github.com/graphql-java-kickstart/graphql-java-servlet/blob/373869b773bf280c1d745d8deb77665defd84929/src/main/java/graphql/servlet/core/internal/ApolloSubscriptionProtocolHandler.java#L74

[codecov-io]

Codecov Report

Merging #371 into master will decrease coverage by 0.09%.
The diff coverage is 92.4%.

@@             Coverage Diff             @@
##             master     #371     +/-   ##
===========================================
- Coverage     94.38%   94.28%   -0.1%     
- Complexity      323      338     +15     
===========================================
  Files            97       99      +2     
  Lines          1139     1207     +68     
  Branches        204      213      +9     
===========================================
+ Hits           1075     1138     +63     
- Misses           22       26      +4     
- Partials         42       43      +1

Impacted Files	Coverage Δ	Complexity Δ
...pring/exception/UknownSubscriptionOperationType.kt	0% <0%> (ø)	0 <0> (?)
...aphql/spring/model/SubscriptionOperationMessage.kt	100% <100%> (ø)	4 <4> (?)
...up/graphql/spring/SubscriptionAutoConfiguration.kt	100% <100%> (ø)	6 <2> (+1)	⬆️
...p/graphql/spring/GraphQLConfigurationProperties.kt	100% <100%> (ø)	3 <0> (ø)	⬇️
...l/spring/execution/SubscriptionWebSocketHandler.kt	85.71% <100%> (-7.15%)	2 <0> (ø)
...ing/execution/ApolloSubscriptionProtocolHandler.kt	92.98% <92.98%> (ø)	11 <11> (?)
.../graphql/generator/extensions/graphQLExtensions.kt	100% <0%> (ø)	0% <0%> (ø)	⬇️
.../graphql/exceptions/NestingNonNullTypeException.kt
... and 2 more

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[smyrick]

Here is an example of the subscriptions working on the playground

[smyrick]

And here is a keep alive example where the client stops the connection