gradle plugin coordinates have changed

when using the _buildscript_ syntax it looks like the plugin coordinates from the gradle portal have changed and now require a `gradle.plugin.` prefix.

so one should now use a synatx like the following:

```
buildscript {
repositories {
maven {
url "https://plugins.gradle.org/m2/"
}
}
dependencies {
classpath "gradle.plugin.fr.brouillard.oss.gradle:gradle-jgitver-plugin:0.4.0"
}
}

apply plugin: "fr.brouillard.oss.gradle.jgitver"
```

Unfortunately this a breaking change, in order to keep the old coordinates one should follow
- https://discuss.gradle.org/t/removing-the-gradle-plugin-prefix-from-a-published-plugin/21973/2
- and new instructions for `mavenCoordinates` in https://plugins.gradle.org/docs/publish-plugin.

Some tests are required to understand the behavior of `mavenCoordinates` and define potentia next steps/stories for the plugin.