Customize tooling_jre with env var

[DatGuyJonathan]

I have a use case where I need tooling_jre to be customizable: https://github.com/redhat-developer/vscode-java/blob/master/src/requirements.ts#L36.

I can't use the embedded ones because I need to use a custom one that has the right certs to work with an internal service. I also can't use java.jdt.ls.java.home because the location of the JRE will depend on which machine it's running on. Also, settings.json doesn't accept env variables.

Is it possible to get tooling_jre from an env var?