chore: add alpine as allowed base image

[FaGru3n]

Description

• add 'alpine' as allowed base-image

updates eclipse-tractusx/sig-infra#259

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[almadigabor]

LGTM

[SebastianBezold]

I think it is ok to merge it, but I'm missing some examples in our unit-tests.
The check is currently just doing a lazy contains. This would allow too many images in my opinion.
So what do we want to allow as base image here? is it plain alpine, or is it every image, that is based on alpine like a postgres alpine image for example?

We should add proper unit-tests with allowed and unallowed examples and enhance the isAllowedBaseImage function

/ping @FaGru3n @almadigabor