Missing docs for add_fields, add_labels, add_tags processors

[andrewkroh]

We recently added some new processors but we don't have documentation for them.

• add_fields - Add fields labels #10119
• add_tags, add_labels - Introduce add_labels and add_tags processors #9973

And once we add documentation I think we can close out:

• Create add_fields processor #7350
• Provide add_fields processor in filebeat #4518

[andrewkroh]

Here's something to get us started.

add_fields

Parameters

• fields - Required.
• target - Optional. Defines where to add the fields. Default is fields. Use empty string to write to the root of the event.

processors:
- add_fields:
    fields:
      hello: world

This would create.

{
  "fields": {"hello": "world"}
}

This add fields to the root.

processors:
- add_fields:
    fields:
      hello: world
    target: ""

And creates:

{"hello": "world"}

add_labels

Parameters

• labels: Required. Labels to add to the event.

processors:
- add_labels:
    labels:
      co.elastic.application: webserver

add_tags

Parameters

• tags: Required. List of tags to append. The processor does not deduplicate tags.
• target: Optional. Default value is tags

processors:
- add_tags:
    tags: ["foo", "bar"]