Add ability to git clone repositories using basic authentication

When trying to clone a non-public repository, a JGit TransportException is thrown. Since the cloning is actually done in the GitManager, there's no way to add authentication manually. JGit is expecting some CredentialsProvider.

I see two possible solutions:

1. Add an overridden getRepository method, that accepts a CredentialsProvider as third argument. In that case the code of the DefaultGitManager should be changed a bit:

                   // Step 2.1: Need to clone the remote repository since it doesn't exist
                   git.cloneRepository()
                       .setDirectory(localDirectory)
                       .setURI(repositoryURI)
                       .setCredentialsProvider(credentialsProvider)   // this line should be added
                       .call();
     

2. Split up the getRepository method and expose a method getLocalGitDirectory, in that case you can choose in a script to only use the getLocalGitDirectory method and do the actual clone yourself. This is probably a more complex change, but it gives more flexibility.