[DOCS] Most Java testing framework docs are not relevant for end users

[jrodewig]

In the Java testing framework docs, we state:

The testing framework allows you to setup clusters with multiple nodes in order to check if your code covers everything needed to run in a cluster.

Users, particularly application developers, could interpret this as the framework giving them the ability to write tests that hit standard ES endpoints from their application.

However, this content is intended for plugin/integration developers. Those developers can use the framework to test their own custom HTTP endpoint (via an ES plugin).

Proposal

At least, we should clarify the intended audience for the testing docs.

We should also consider migrating the docs to the Plugins and integrations docs, perhaps as a subpage of Help for plugin authors.

[elasticmachine]

Pinging @elastic/es-docs (>docs)

[elasticmachine]

Pinging @elastic/es-core-infra (:Core/Infra/Plugins)

[jrodewig]

The team discussed this and decided that removing the Java testing framework docs was
the best course of action. The current docs are very outdated and plugin authors will likely
need more specific guidance.