external: Restructure external cluster examples manifests (backport #13932)

[mergify[bot]]

This PR will add separate directory to handle the external manifest. All the files under examples are kept same, so that the CI and tests are not broken. Resolves #12599

Checklist:

• [x] Commit Message Formatting: Commit titles and messages follow guidelines in the developer guide.
• [x] Reviewed the developer guide on Submitting a Pull Request
• [x] Pending release notes updated with breaking and/or notable changes for the next minor release.
• [x] Documentation has been updated, if necessary.
• [x] Unit tests have been added, if necessary.
• [x] Integration tests have been added, if necessary.

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  This is an automatic backport of pull request #13932 done by Mergify.