Ignore https errors

[andrewvc]

Fixes #27202

NOTE: This requires a version of synthetics with elastic/synthetics#361

Adds an option to disable errors on invalid TLS certificates in heartbeat.

Rather than try to work with ssl.verification_mode: none this adds a new option. The reason being that the behavior here is just too different to share a configuration option.

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

Badssl targets should function

- id: test
  name: A Test
  type: browser
  schedule: "@every 10s"
  ignore_https_errors: true
  source:
    inline:
      script: |-
       step('Go to home page', async () => {
         await page.goto('https://expired.badssl.com/');
       });  

[elasticmachine]

Pinging @elastic/uptime (Team:Uptime)

[elasticmachine]

💚 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

• Start Time: 2021-08-17T02:45:45.921+0000

• Duration: 66 min 45 sec

• Commit: 647bd45

Test stats 🧪

Test	Results
Failed	0
Passed	3389
Skipped	80
Total	3469

Trends 🧪

💚 Flaky test report

Tests succeeded.

Expand to view the summary

Test stats 🧪

Test	Results
Failed	0
Passed	3389
Skipped	80
Total	3469

[vigneshshanmugam]

LGTM

[andrewvc]

@Mergifyio backport 7.x

[mergify]

Command backport 7.x: success

Backports have been created

• #27425 Ignore https errors (backport #27412) has been created for branch 7.x