[Feature] Support JDK toolchains plugin in spotless maven plugin

[HuangFru]

Spotless can not sense the toolchains plugin in Maven.

I have different Java versions in my project and use Spotless to be the checkstyle plugin. Also, I use the JDK toolchains maven plugin to help me pick different JDK env in different modules. But when I built the whole project, Spotless can not sense the toolchains, so it used the wrong JDK to apply Spotless(different modules have different Google Java formats to support different JDK).

I'm willing to submit a PR, but I wonder if the communications can merge it into older versions such as 2.30.0 or a branch that supports JAVA 8(cause I have Java 8 env).

[nedtwigg]

A PR for toolchains support is very welcome.

Re: Java 8 - we will not release any new versions for Java 8. But feel free to fork or use JitPack and link to it from here if you need Java 8 support.