Summary

Extend the ClusterLogForwarder to support Splunk metadata fields when forwarding logs
so that we enable better integration with Splunk.

Acceptance Criteria

• Verify the Collector sets the `host` when forwarding logs to the value of `hostname`
• Verify the ClusterLogForwarder API has fields that allows setting `source` using the ClusterLogForwarder templating
• Verify the ClusterLogForwarder API has fields that allows setting `index_fields` using path syntax
• Verify the Collector sets `host`, `source`, `sourcetype` with Red Hat 'defaults' when not otherwise spec'd in the ClusterLogForwarder
• Verify the Collector forwards logs with the desired data when the metadata fields are set in the API

Notes

• Defining default values for those keys when not specified by the user.
• Supporting user configuration of these metadata keys via templating mechanisms.
• Work around some limitations by transforming field names and values before forwarding.
  • Nested fields must be flattened into top-level fields.
  • Unsupported characters replacing with underscores (_).
  • Non-string values converting to strings.
  • Objects serializing to JSON strings.