Support multiple endpoints

[janfuhrer]

Support multiple endpoints with one exporter like the prometheus-pve-exporter.

- job_name: 'pbs-exporter'
  static_configs:
    - targets:
      - <target-ip-1>
      - <target-ip-2>
  metrics_path: /metrics
  params:
    module: [default]
  relabel_configs:
    - source_labels: [__address__]
      target_label: __param_target
    - source_labels: [__param_target]
      target_label: instance
    - target_label: __address__
      replacement: pbs-exporter:9101