[DOCS] Updated Heartbeat screenshot

[ugosan]

What does this PR do?

Updates the rather dated screenshot for Heartbeat in "Heartbeat quick start: installation and configuration" page

Why is it important?

The old screenshot just shows a dashboard that doesn't highlight our current UI for Heartbeat data (Uptime)

Checklist

• [ ] My code follows the style guidelines of this project
• [ ] I have commented my code, particularly in hard-to-understand areas
• [x] 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.

[elasticmachine]

Pinging @elastic/obs-docs (Team:Docs)

[elasticmachine]

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• Start Time: 2022-08-05T17:03:46.200+0000

• Duration: 50 min 9 sec

Test stats :test_tube:

Test	Results
Failed	0
Passed	1493
Skipped	22
Total	1515

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Tests succeeded.

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[bmorelli25]

Thanks, @ugosan!

I wonder if we should also update step seven (View your data in Kibana) of the quick start? The step mentions Kibana dashboards and the uptime-contrib repo, but not the Uptime app.

cc @colleenmcginnis as this is her area of expertise.

[mergify[bot]]

This pull request does not have a backport label. If this is a bug or security fix, could you label this PR @ugosan? 🙏. For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change) To fixup this pull request, you need to add the backport labels for the needed branches, such as:
• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit

[mergify[bot]]

This pull request does not have a backport label. If this is a bug or security fix, could you label this PR @ugosan? 🙏. For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed branches, such as:

• backport-v8./d.0 is the label to automatically backport to the 8./d branch. /d is the digit