Heartbeat: add support for pushed monitor source

[vigneshshanmugam]

• fix [Heartbeat] Introduce new source for pushed monitors #31363
• Adds the new source for the pushed monitors from Synthetics - feat: bundle and push all journeys to kibana synthetics#482
• The pushed monitor would be in the below format

heartbeat.monitors:
  - type: browser
    id: my-monitor
    name: My Monitor
    source:
      pushed:
        content: // base 64 encoded content linking to the bundled source
    schedule: "@every 1m"

• This content would then be base64 decoded and unzipped in to the directory structure that was used to upload the monitors from the Synthetics command. HB basically does the reverse of what Synthetics CLI has done for uploading the monitors.

TODO

• Docs on the pushed monitor source, however we can do that separately once synthetics is ready

[elasticmachine]

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• Start Time: 2022-05-12T22:46:42.060+0000

• Duration: 39 min 1 sec

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Passed	135
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Total	135

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[elasticmachine]

Pinging @elastic/uptime (Team:Uptime)

[lucasfcosta]

Overall it LGTM but I would prefer to deal with the zipslip thing before merging this one in. Excellent work, I really like the tests (nice setup/teardown with the subtests too).

I have also E2E tested this PR by:

1. Creating the following journey:

   import { journey, step, monitor } from "@elastic/synthetics";
   journey("latency", ({ page }) => {
     monitor.use({});
     step("load homepage", async () => {
       await page.goto("https://google.com");
     });
     step("wait for test", async () => {
       await page.waitForTimeout(2e3);
     });
   });

2. I used this PR to bundle it into a zip
3. Got the base64 encoded content

   base64 ~/bla.zip | pbcopy
   

4. Created this monitor in Heartbeat pointing to my local Kibana

   - type: browser
     id: my-monitor
     name: My Monitor
     schedule: '@every 1m'
     source:
       pushed:
         content: 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

5. Checked Kibana and saw results there 🎉

PS: Ideally one must either use a new locally built version of the agent or not use monitor.use to avoid the monitor failing.

[lucasfcosta]

Shouldn't we also defer the close of this file? Although we're already removing it the docs don't mention Remove closes the open handle.

PS: I found it interesting to learn how these are made to be globally unique

[vigneshshanmugam]

Its explicity handled after the monitor run to completion, we control the close using p.Close() on any error and remove these unzipped directories.

[lucasfcosta]

LGTM, thanks for the zipslip update!