[Manual backport][Heartbeat] Enable engine strict validation

[emilioalvap]

What does this PR do?

Manual backport of elastic/elastic-agent#2225 and #34470.
Enable engine strict validation when bundling synthetics.

Why is it important?

https://discuss.elastic.co/t/synthetic-browser-tests-are-failing-in-version-7-x/324440/8

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

Change node installed version to NODE_VERSION=13.1.0 and build heartbeat docker image locally. It should fail with:

#22 2.226 npm verb stack Error: Unsupported engine for @elastic/synthetics@1.0.0-beta.40: wanted: {"node":">14.14.0"} (current: {"node":"13.1.0","npm":"6.12.1"})

[elasticmachine]

Pinging @elastic/uptime (Team:Uptime)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Start Time: 2023-02-27T17:41:58.586+0000

• Duration: 200 min 14 sec

Test stats 🧪

Test	Results
Failed	0
Passed	22239
Skipped	1566
Total	23805

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages and run the E2E tests.

• /beats-tester : Run the installation tests with beats-tester.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[andrewvc]

LGTM

[emilioalvap]

/test

[emilioalvap]

/test

[emilioalvap]

Test failures are unrelated, fix coming from #34501.

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b hb-backport-engine-strict upstream/hb-backport-engine-strict
git merge upstream/7.17
git push upstream hb-backport-engine-strict