Remove legacy modules

[paulbakker]

Preview branch removing all legacy modules. This will be merged in late 2024. From then on, the DGS/Spring GraphQL integration will be the only implementation.

Test with the Release Candidate

We published 10.0.0-rc.1 as the first Release Candidate based on this branch.
To test with the RC, add the following repository to your build.gradle (or Maven equivalent).

repositories {
 maven {
        name = "OSS Candidates"
        url = "https://artifacts-oss.netflix.net/artifactory/maven-oss-candidates"
    }
}

### Details of changes
The following modules are completely removed because they are replaced by Spring GraphQL. If you were already using the com.netflix.graphql.dgs:graphql-dgs-spring-graphql-starter (Spring GraphQL integration) you were already not using any of these modules.

Deleted modules:

• graphql-dgs-spring-boot-oss-autoconfigure
• graphql-dgs-spring-webmvc
• graphql-dgs-spring-webmvc-autoconfigure
• graphql-dgs-spring-boot-starter
• graphql-dgs-example-java
• graphql-dgs-example-java-webflux
• graphql-dgs-subscriptions-websockets
• graphql-dgs-subscriptions-websockets-autoconfigure
• graphql-dgs-subscriptions-graphql-sse
• graphql-dgs-subscriptions-graphql-sse-autoconfigure
• graphql-dgs-subscriptions-sse
• graphql-dgs-subscriptions-sse-autoconfigure
• graphql-dgs-spring-webflux-autoconfigure
• graphql-dgs-webflux-starter

Deleted classes:

• DgsAutoConfiguration: Autoconfiguration classes have moved. This may break tests that are using @SpringBootTest(classes = {DgsAutoConfiguration.class, ...}, and should use @EnableDgsTest instead.
• DefaultGraphQLClient: This is a long deprecated class that has been replaced by [CustomGraphQLClient, CustomReactiveGraphQLClient and WebClientGraphQLClient.
• DefaultDgsReactiveQueryExecutor: There should be no user impact because its interface should be used instead.
• DefaultDgsQueryExecutor: There should be no user impact because its interface should be used instead.

Other changes

• Subscriptions over SSE in Spring GraphQL are using the newer, more official GraphQL over SSE RFC spec. The old spec is no longer supported by DGS.
• If you are using SSESubscriptionGraphQLClient in tests to test your DGS server, switch to GraphqlSSESubscriptionGraphQLClient, which has the same interface, but uses the new protocol.
• SSESubscriptionGraphQLClient can still be used to call into other services using the old protocol, but this client is now deprecated for removal in the future.
• Note that Spring GraphQL serves subscriptions on the /graphql endpoint, not on the /subscriptions endpoint like DGS used to do.

[paulbakker]

@srinivasankavitha @kilink Preparing this branch for onboarding purposes. Not ready to merge yet, but it's a preview of things to come.
Note that I've disabled some client SSE/WS tests for now, need to replace some things in the setup with Spring GraphQL to get those to work.

[srinivasankavitha]

Looks good to me. I've noticed quite a few projects that add graphql-dgs-spring-boot-starter as a dependency in their build.gradle files in addition to the starter. This is incorrect usage in any case. Calling it out explicitly so we are not surprised by breakages there.

[iparadiso]

More curious than an actual comment, but why did the (c) get adjusted back in time? Should this be a SED to bump them up to 2024?

[paulbakker]

Weird, I have no idea. The copyright header comes from a profile in Intellij, which has $today.year as a variable. After this is merged with can do a clean up.