[notifications] flaky test analyser

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We would like to provide a flaky test analyser reporting as a GH comment for all the PRs for a given project.

For such, the automation in place should raise an issue for each flaky test match, unless there is an existing issue for that particular flaky test.

The notification should always be reported even when there are test failures without a flaky test, this will always help to audit and track every PR.

What are the components that are required?

• Component to look up for any open issues that match the given flaky test.
  • This component will return a dictionary with all the flaky tests and their GH issues if any or empty if nothing.
• Component to create issues for the given flaky test if it does not exist. There will be a template issue.
• Component to decorate the GH comment with the given list of flaky tests and their issues (the ones that already exist or the new ones that were created.

How does it work?

notifyBuildResult step will be the wrapper with the arguments analyzeFlakey

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The below are the examples notifications we will use:

🐛 Flaky test report

❕ There are not known flaky tests.

And issues creations with the below format:

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See elastic/beats#21853