RM: upgraded wrapper to gradle 7.6, and removed obsolete plugin import

We are using pjlsa at GSI ( @mihostet and @oeftiger were involved in that ), that internally used the cmmnbuild-dep-manager to resolve its Java dependencies. GSI is currently already using Java 17 and the current gradle-wrapper used in cmmnbuild-dep-manager only supports up to Java 10:

Welcome to Gradle 4.7!

Here are the highlights of this release:
 - Incremental annotation processing
 - JDK 10 support
 - Grouped non-interactive console logs
 - Failed tests are re-run first for quicker feedback

This is a merge request to update the gradle-wrapper to the latest gradle version (7.6).

I had to make a small modification to the gradle.py resolver since the "maven" plugin is obsolete and integrated into the "maven-publish" plugin.

I also checked the gradle matrix ( https://docs.gradle.org/current/userguide/compatibility.html ) and it should still run with Java 8 and still compile even Java 6.

Would it be possible to update the wrapper?