Add template for Flatcar clusters

[johananl]

What this PR does / why we need it: This PR adds a cluster template for workload clusters running Flatcar Container Linux.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): None

Special notes for your reviewer: None

Release notes:

Add cluster template for workload clusters running Flatcar Container Linux

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: johananl
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[coveralls]

Pull Request Test Coverage Report for Build 12691238299

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 59.245%

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Totals
Change from base Build 11667377340:	0.0%
Covered Lines:	1570
Relevant Lines:	2650

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💛 - Coveralls

[johananl]

• TODO: Authorize SSH key on nodes.