Add insecure option to Prometheus provider

[OpenGuidou]

Summary

Similarly to what's available in the web analysis provider, it would be useful to have the possibility to skip the TLS verification on prometheus endpoint.

Use Cases

provider:
  prometheus:
    address: https://prometheus.example.com
    insecure: true
    query: |
      sum(irate(
        istio_requests_total{reporter="source",destination_service=~"{{args.service-name}}",response_code!~"5.*"}[5m]
      )) /
      sum(irate(
        istio_requests_total{reporter="source",destination_service=~"{{args.service-name}}"}[5m]
      ))

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