feat: capture performance metrics from trace events

[vigneshshanmugam]

• fixes Capture relevant perf metrics to close the gap with RUM agent #120
• Captures FirstContentfulPaint, LongestContentful Paint, Navigationorigin, Dom content loaded, Load event, Layout shift events, Cumulative Layout shift from chrome trace events
• Replace trace flag with filmstrips in the CLI.
• Writes to the JSON reporter as journey/metrics to reflect the trace output timing information.
• Uses the Lighthouse Trace processor to extract the events specific to the current main process.
• included Notice.txt which ppints to Lighthouse license as we are using their trace processor for extracting key metrics.

Trace output is in this format

{
  "type": "journey/metrics",
  "@timestamp": 1622578544529441,
  "journey": {
    "name": "check if input placeholder is correct",
    "id": "check if input placeholder is correct"
  },
  "root_fields": {
    "browser": {
      "experience": {
        "name": "navigationStart",
        "type": "mark",
        "start": 1014038.407051
      }
    },
    "os": {
      "platform": "darwin"
    },
    "package": {
      "name": "@elastic/synthetics",
      "version": "1.0.0-beta.2"
    }
  },
  "package_version": "1.0.0-beta.2"
}

start, end - Timings that are relative to step/journey start and end times.

[apmmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Build Cause: Started by user Vignesh Shanmugam

• Start Time: 2021-06-01T20:15:02.323+0000

• Duration: 13 min 42 sec

• Commit: 432e791

Test stats 🧪

Test	Results
Failed	0
Passed	96
Skipped	0
Total	96

Trends 🧪

[andrewvc]

Leaving a partial review here will follow up with a complete review ASAP

[andrewvc]

FYI I did reach out to @drewpost and discuss the fact that metrics we collect are not aligned up with lighthouse or many other tools due to the fact that specific browser versions and platform differences will prevent numbers from lining up exactly.

Once this is merged we should be sure sure to document these differences and explain performance in the synthetics documentation. I've opened elastic/observability-docs#735 to track

[vigneshshanmugam]

@andrewvc Thanks Andrew for taking care of that and the info.

[andrewvc]

LGTM however I'll leave it up to you to determine whether you want to move the fields out of the payload now or in a subsequent PR. We can't build GUI features based on this until we have proper elasticsearch fields defined in our mappings.

[andrewvc]

LGTM