feat: add labels meta

[shahzad31]

Allows the ability to add meta via labels.* fields

fixes #729 !!

This will only work with kibana 8.16.0 with PR elastic/kibana#193250 !!

  monitor.use({
    id: 'example-monitor',
    schedule: 10,
    labels: {
      foo: 'bar',
      team: 'synthetics',
    }
  });

lightweight

heartbeat.monitors:
- type: http
  name: Todos Lightweight
  id: "todos- light  weightt
  enabled: true
  urls: "https://elastic.github.io/synthetics-demo"
  schedule: '@every 3m10s'
  timeout: 16s
  alert.status.enabled: true
  labels.environment: "production"
  labels.team: "todos"

[emilioalvap]

@shahzad31 I'm worried this will confusing since the lightweight representation is not a valid heartbeat monitor and effectively undocumented, wdyt?

[shahzad31]

@shahzad31 I'm worried this will confusing since the lightweight representation is not a valid heartbeat monitor and effectively undocumented, wdyt?

@emilioalvap i will create a docs issue in a follow up to document this.

[emilioalvap]

Please add this new field to some of the unit tests validating lightweight monitors

[shahzad31]

i have added here 200e52f (#959)

[vigneshshanmugam]

Let's rename this to fields to map with the heartbeat top level fields name and under the hood in Kibana, you can map to labels. Having labels as top level is confusing - https://www.elastic.co/guide/en/beats/heartbeat/8.12/configuration-general-options.html#libbeat-configuration-fields

Also let's write JS doc annotation so it's visible on TS config.

[vigneshshanmugam]

Let's add test for browser monitor as well.