Closes #7570

Reason for Proposed Changes

• The support for alpine in checkmarx/kics:alpine Docker tag was no longer available which included the apk package manager, which broke scripts relying on Alpine-based behavior. This occurred because the image previously tagged as alpine was actually based on Wolfi Linux, which does not support apk. The tag was misleading and caused confusion for users expecting a real Alpine Linux base (according to the official documentation).

Proposed Changes

• Fix misleading alpine tag:
  • Created a proper Dockerfile.alpine using Alpine Linux with apk support;
  • Now, the alpine tag points to a real Alpine image, resolving the user-reported issue;
• Updated Docker build workflows:
  • latest and v{VERSION} → still use the Wolfi-based image;
  • alpine and v{VERSION}-alpine → now use the new Alpine-based Dockerfile;
  • Updated both release and nightly workflows to support this separation;
• Alpine image now aligns with other Dockerfile variants (debian and ubi);
• Alpine image now included in the Go E2E test matrix;
• Documentation improvements:
  • Added/updated three docs to clearly describe the different image variants and use-cases (docs/dockerhub.md, docs/documentation.md, docs/getting-started.md);

I submit this contribution under the Apache-2.0 license.