Unclear how to use a different JDK for application/server than for running IDEA itself

[scottkurz]

Since the IDE itself seems to require Java 17, it could be necessary to run with a different JDK in order to run an app requiring a different Java level, eg Java 8.

It seems like the options could depend on what else is implemented:

• At the moment, the IDEA Liberty Tools user could set JAVA_HOME env var
• The project JDK setting seems like a good solution: Support common IntelliJ Java "SDK" preference on Run Configuration #177

We probably won't implement toolchain support in the near term but that's another approach: OpenLiberty/ci.gradle#792

So this could be a doc issue at least.

[TrevCraw]

Document each of the JVM's that are in use, how each can be configured, and why users may want to configure them.