Support Maven jdk toolchain config in dev mode

[scottkurz]

Parallel to OpenLiberty/ci.gradle#792, add support for Maven toolchains https://maven.apache.org/plugins/maven-toolchains-plugin/ to independently set the JDK used to run Maven itself vs. the JDK used to run other goals, most importantly (but not exclusively) the Liberty server.

See discussion especially here.

Some dimensions to the problem:

• Honor the configuration of the toolchain plugin itself for plugin goal invocation
• Honor configuration of individual plugins with jdk toolchain config, for executing goals of those plugins
• Honor the config when dev mode executes a Java/JDK invocation outside of executing maven plugins,e.g. when we do the javac recompile in Maven dev mode.

The last is perhaps debatable? So maybe a bit of design thought is needed before proceeding.

[bmarwell]

I would be happy to create a PR once there is a user request (please 👍🏻 if you would like to see it).

[scottkurz]

I would be happy to create a PR once there is a user request (please 👍🏻 if you would like to see it).

Sorry I didn't respond to this before. If/whenever you still have the time and interest, that would be great. I would be happy to collaborate on this.

We actually did get a request just recently:
#1781