[Heartbeat] Always use synthetics data streams for browser

[andrewvc]

A frequent UX issue for our users is wanting to set different retention periods for network / screenshot data. Our default settings for browser monitors really hurt here since we lump them all into a heartbeat data stream unless users are using fleet. This addresses this issue by defaulting browser monitors to use synthetics* data streams which breaks them out by type.

We can't do this in any sort of simple way with the 'heartbeat' prefix. This shouldn't be a practical issue for most users since in 8.x all kibana clusters have synthetics templates pre-installed. Users who have explicitly set their kibana index pattern to only heartbeat-* with no synthetics-* will be affected. Given that we are in beta this potential breakage is worth it for the long term benefits to users.

This also implies Kibana has been setup with Elasticsearch, which is overwhelmingly the case. If kibana is not setup then the mappings for this synthetics index will be incorrect, but this is likely not a real-world concern.

See also elastic/observability-docs#1944

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

Check against a fresh stack with the synthetics integration not installed.

[elasticmachine]

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• Start Time: 2022-06-23T21:16:25.646+0000

• Duration: 49 min 13 sec

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[emilioalvap]

LGTM, tested with a fresh install and heartbeat.yml config only. Browser monitor is configured to use synthetics-*, unlike other types of monitors. Synthetics data view:

HB data view:

Tested with:

heartbeat.monitors:
- type: http
  enabled: true
  id: my-monitor
  name: My Monitor
  urls: ["http://localhost:9200"]
  schedule: '@every 1m'
- type: icmp
  enabled: true
  id: my-monitor-2
  schedule: "@every 1m"
  hosts: [8.8.8.8]
- type: tcp
  enabled: true
  id: my-monitor-3
  schedule: "@every 1m"
  hosts: ["google.es"]
- type: browser
  enabled: true
  id: my-monitor-4
  schedule: "@every 1m"
  name: "My monitor 2"
  source:
    inline:
      script: |
         step("load homepage", async () => {
           await page.goto('https://www.elastic.co');
         });

[elasticmachine]

Pinging @elastic/uptime (Team:Uptime)

[dominiqueclarke]

LGTM. Data for browser monitors was properly segmented into data streams. No data was written to heartbeat.