[heartbeat] Add support for ubi8-complete image

[andrewvc]

WIP experimental support for UBI8 in complete image

What does this PR do?

Why is it important?

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.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

Use cases

Screenshots

Logs

[mergify]

This pull request does not have a backport label. Could you fix it @andrewvc? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

💔 Build Failed

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: 2021-10-21T21:15:58.628+0000

• Duration: 33 min 38 sec

• Commit: 2e9fe8a

Test stats 🧪

Test	Results
Failed	0
Passed	3
Skipped	0
Total	3

Steps errors

Expand to view the steps failures

Error signal

• Took 0 min 0 sec . View more details here
• Description: Error 'java.io.NotSerializableException: java.util.regex.Matcher'

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

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.

[mdelapenya]

Before merging this PR, please consider revisiting the variants attribute, as we suggest in #28526, where we define a new "variant" (the complete, or any other, such as the cloud one) directly in the declarative way (using packages.yml) Vs doing it in a programmatic manner (using dockerbuilder.go)

[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 ubi8-complete upstream/ubi8-complete
git merge upstream/master
git push upstream ubi8-complete

[andrewvc]

Closing in favor of #29255