Use release jvm option to build artifact compatible with older JVM.

[sbernard31]

For many reason, we decide to produce jar compatible :

• with Java8 for Leshan 2.0.0
• with java7 for Leshan 1.0.0

By the past, when we tried to create binaries compatible with older version of java than the one used to build, we face some compatibility issue.
(e.g. using java8 to build java7 compatible jar)

This lead us to either :

• use maven toolchain but this make the build more complicated to use.
• use same JVM to launch the build than the targeted one, but more and more maven-plugin change their minimal java requirement to java11.

Recently, I heard about jvm --release option, maybe this could solve this issue :

• https://bugs.openjdk.org/browse/JDK-8058150
• https://www.baeldung.com/java-compiler-release-option
• https://stackoverflow.com/questions/59049980/maven-compiler-release-as-an-replacement-for-source-and-target

[sbernard31]

Fixed by :

• modify maven build to use JVM release option  #1494
• modify maven build to use JVM release option for branch 1.x #1495

[sbernard31]

⚠️ Eclipse user could face some issue with this new configuraiton way because of an m2e bugs which should be fixed in next release (v2.4.0), See eclipse-m2e/m2e-core#1509 ⚠️