add goss tests for capi images

[mac641]

Description

close #355

Used AI-Tools ✨

• inspiration for test cases were generated by Mistral 3

[vknabel]

Is the FRR tested for the other images in comparable tests? If yes, we might add those, too.
In general all not-Gardener-specific tests should be applicable here. Are there any?

[mac641]

Is the FRR tested for the other images in comparable tests? If yes, we might add those, too. In general all not-Gardener-specific tests should be applicable here. Are there any?

The capi tests are just an addon. All remaining tests are still executed.
And it looks like there's a check for frr in the main test file: https://github.com/metal-stack/metal-images/blob/master/test/sut-ctx/home/metal/inputs/goss.yaml#L106-L108