Remove Actions cache from release (ExpediaGroup#578)

The step actions/cache does not support the release event.

See: https://github.com/actions/cache/blob/b45d91cc4bac5c58ff24b19cd3b6711b2c5eca8f/src/utils/actionUtils.ts\#L98
And our logs: https://github.com/ExpediaGroup/graphql-kotlin/runs/408004612\?check_suite_focus\=true\#step:5:10

Remove perf-tests directory (ExpediaGroup#576)

We are not using these tests in any of our build processes. They were added to help debug if we had any subscription issues. If we want to add tests back in we should do that through Kotlin and the gradle build.

Remove perf-tests directory (ExpediaGroup#576)

We are not using these tests in any of our build processes. They were added to help debug if we had any subscription issues. If we want to add tests back in we should do that through Kotlin and the gradle build.

Remove perf-tests directory (ExpediaGroup#576)

We are not using these tests in any of our build processes. They were added to help debug if we had any subscription issues. If we want to add tests back in we should do that through Kotlin and the gradle build.

[build] apply nexus-publish plugin on ALL projects (ExpediaGroup#567)

It appears that maven-publish plugin will skip its execution if repositories are not configured in given project. Changing the configuration to apply nexus-publish plugin on all projects.

[build] explicitly configure nexus-publish-plugin on root project (Ex…

…pediaGroup#563)

Gradle `publish` task now explicitly depends on the `initializeSonatypeStagingRepository` task from `nexus-publish-plugin`. We need to explicitly set this as we are not publishing any artifacts from the root project.

[build] configure GH action PR check for documentation updates (Exped…

…iaGroup#549)

* [build] configure GH action PR check for documentation updates

Github Action checks out the repository and attempts to run [docusaurus-build](https://docusaurus.io/docs/en/commands#docusaurus-build) command.

* limit PR check to just docs and website directories

Delete publish package GH Action (ExpediaGroup#482)

Disable the GH action for now to publish to GH Package Registry

Validate subscription return type (ExpediaGroup#476)

Subscriptions must return a org.reactivestreams.Publisher for graphql-java to work properly. An exception will now be thrown if any return type of a top level subscription is not a subclass of Publisher

Fixes ExpediaGroup#359

build: 1.3.1-SNAPSHOT (Travis Build 1294) (ExpediaGroup#461)