update project to support JDK 17 and Gradle 7

[SingingBush]

The gradle plugin will need some changes to work with current versions of Gradle and Java. I created #3 as an initial step toward this and if merged will make the required changes to get the build working with Java 17 as well.

[SingingBush]

I've raised opened #5 which includes #3 and will resolve this issue. The CI builds with versions of Java from 8 to 18