Unify git access

[metacosm]

We're currently using 2 different git libs and since, right now, we've tied ourselves to GitHub with the reporting, we should probably only use the GitHub library.

[cmoulliard]

Can we also upgrade the git lib to use the quarkus git extension please instead of the following deps ?

<!-- git -->
        <dependency>
            <groupId>org.eclipse.jgit</groupId>
            <artifactId>org.eclipse.jgit</artifactId>
        </dependency>

        <dependency>
            <groupId>org.kohsuke</groupId>
            <artifactId>github-api</artifactId>
            <version>${kohsuke.version}</version>
        </dependency>