No documentation on JVM parameters for CLI

Latest docs do not have any documentation on how to add JVM parameters to the CLI interface. If they do, I've been unable to find them with terms I'd expect to use.

Compare [latest](//grails.github.io/grails-doc/latest/guide/commandLine.html) to [2.3.x](//grails.github.io/grails-doc/2.3.x/guide/commandLine.html).

Notably, words like `memory` `jvm` `system property` should be included in the description, for searchability. I'd also recommend `GRAILS_OPTS`, as that was applicable for 2.3.x environments.

If it's no longer supported, that information should be accessible in the [upgrading](//grails.github.io/grails-doc/latest/guide/upgrading.html).

The closest I've found was searching for system properties, which yielded the page on [`run-app`](//grails.github.io/grails-doc/latest/ref/Command%20Line/run-app.html). I tested the `server.port` example and it did nothing. I attempted `grails.server.port.http` but that led to a cryptic error, which I'm not prepared to investigate.

Compare the latest and 2.3.x guide/commandLine.html pages, then review the run-app and upgrading documentation linked in the issue. Determine whether JVM parameters and GRAILS_OPTS are supported; document the supported usage and searchable terms, or explain the removal in upgrading.html.

Written by the indexing model from the issue text.