GCP stackdriver producer

[arnecls]

The purpose of this pull request

This adds a producer for google stackdriver logs.

Config to verify

Messages passed to stdin have to be formatted as severity: payload, e.g. Warning: {"text":"Hello World"}. JSON parsing is optional, i.e. if you pass the "message" payload to Stackdriver, it will be passed as JSON if it begins with a { or else as text.

stdIn:
  Type: consumer.Console
  Streams: "stdin"
  Modulators:
  - format.Hostname:
      ApplyTo: "host"
      Separator: ""
  - format.Grok:
      Patterns:
        - "^(?P<severity>[^:]+?): (?P<message>.*?)$"
  - format.JSON:
      Source: "message"
      Target: "json"

stdOut:
  Type: producer.Console
  Streams: "stdin"
  Modulators:
  - format.ToJSON: {}

stackdriver:
  Type: producer.Stackdriver
  Streams: "stdin"
  ProjectID: "trv-hs-kubernetes-edge"
  Payload: "json" # can also use message
  Severity: "severity"
  DefaultSeverity: "Info"
  LogName:
    "stdin": "application-logs"
  Labels:
    - "host"

Checklist

• make test executed successfully
• unit test provided
• integration test provided
• docs updated