Refactor, change input, add output formats and drop external services

[yann-soubeyrand]

• Configuration has been refactored: it is now organized in group of options.
• Puppetdb input source has been switched from custom fact to Prometheus::Scrape_job resource.
• New output formats have been added: in addition to a unique static_config list, a list of scrape_configs or a list of static_config by job can now be outputted.
• Kubernets configmap output has been modified to become a Kubernetes secret output.
• Experimental Kubernetes external services output method has been dropped: it didn't work well in a lot of cases.