Extend Dockerfile based build strategies with target build stage

[SaschaSchwarze0]

Changes

I recently stumbled over a single Dockerfile that combined multiple output images and one had to run docker build --target STAGE to select which one should actually be built. And that was not possible with our sample build strategies because we had no parameter for the target stage. Adding this. Related Dockerfile feature: https://docs.docker.com/build/building/multi-stage/#stop-at-a-specific-build-stage

Submitter Checklist

• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
• Set a kind label on this PR
• Release notes block has been filled in, or marked NONE

Release Notes

The Dockerfile-based sample build strategies for BuildAh, BuildKit and Kaniko now have a target parameter to define the stage to be built

[qu1queee]

very interesting, can you reference https://docs.docker.com/build/building/multi-stage/#stop-at-a-specific-build-stage in the above PR description. What are the use cases on this for SHP users?

[qu1queee]

/lgtm

[SaschaSchwarze0]

What are the use cases on this for SHP users?

The Dockerfile that I had stumbled over this is https://github.com/ONLYOFFICE/Docker-Docs/blob/v8.2.1-1/Dockerfile. It is a single Dockerfile that you must run for targets like proxy, converter or docservice to produce the different images you need for onlyoffice.

[SaschaSchwarze0]

Added e2e test cases.

[qu1queee]

/lgtm
/approve

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