KAFKA-14198: Define separate swagger configuration in Gradle build

[C0urante]

Follow-up from #12609. Non-urgent, just tidies up the build file a bit.

Tested and verified locally by:

1. Running ./gradlew releaseTarGz and then examining the resulting release artifact with tar tf tar tf core/build/distributions/kafka_2.13-3.4.0-SNAPSHOT.tgz to ensure that it did not contain the swaggerJaxrs2 jar or its dependencies
2. Running ./gradlew siteDocsTar and then examining the resulting docs with cat docs/generated/connect_rest.yaml to ensure that all Connect REST endpoints were included.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[ijuma]

Do we need this to be implementation or can it be swagger too?

[C0urante]

I gave this a try but it wasn't successful. We still need the annotations at compile time since they're used to decorate our REST resource classes, like here:

kafka/connect/runtime/src/main/java/org/apache/kafka/connect/runtime/rest/resources/ConnectorsResource.java

Lines 108 to 114 in b449b80

	@GET
	@Path("/")
	@Operation(summary = "List all active connectors")
	public Response listConnectors(
	final @Context UriInfo uriInfo,
	final @Context HttpHeaders headers
	) {

[ijuma]

Do we need this assignment at all or can we just inline it?

[C0urante]

The plugin requires the classpath field to be set.

I also tried this:

classpath = sourceSets.main.runtimeClasspath + configurations.swagger.asCollection()

buildClasspath = classpath

which led to a lot of these warnings:

Gradle detected a problem with the following location... Reason: Task ':connect:runtime:genConnectOpenAPIDocs' uses this output of task ':connect:runtime:processResources' without declaring an explicit or implicit dependency.

Based on discussion in the PR that introduced OpenAPI docs generation for Connect, it appears that setting classpath to sourceSets.main.runtimeClasspath creates some implicit dependencies for the genConnectOpenAPIDocs task that fix these warnings.

[ijuma]

Thanks @C0urante. Did you verify that the documentation is still generated correctly and the release tarball still doesn't have swagger and snakyaml in the dependencies?

[C0urante]

Thanks @ijuma. Yes, I verified both, and updated the PR description with the steps I took to do so.

[ijuma]

LGTM, thanks.

[C0urante]

Thanks Ismael. Kicked off another Jenkins build since the previous one failed with a disk space error; will merge if everything looks alright.

[C0urante]

Failures appear unrelated, merging.

[C0urante]

@ijuma @jsancio I'm assuming we don't need to backport this to 3.3 since the immediate issues with Swagger deps and Connect OpenAPI docs generation have already been fixed on that branch; let me know if that's not the case, though.