Content type application/graphql+json

[juergenzimmermann]

Describe the bug
js-graphql-intellij-plugin submits the POST requests with the header Accept: application/json. However, according to the GraphQL spec the header should use application/graphql+json. Using application/json is considered as legacy. See https://github.com/graphql/graphql-over-http/blob/main/spec/GraphQLOverHTTP.md#content-types.

Expected behavior
The request header should contain application/graphql+json.

Version and Environment Details
Operation system: Windows 11 21H2
IDE name and version: IntelliJ IDEA Ultimate 2022.1
Plugin version: 3.1.3

[martinbonnin]

Note that the current draft moved to application/graphql-response+json