Migrate from Drone to GH Actions

[andreas-kupries]

Fix rancher/rancher#44988

Added draft GHA flows for test builds, and publication.

🚧 ⚠️ ⚠️ 🚧

• Test the flows. Although unclear how to do that for the publication flow. The problem is less that it cannot be triggered for testing, enabling manual triggers handles that nicely. The issue is that the flow will push non-release images to the docker hub, which is very much not desired. That said, it also requires secrets, which we do not have yet.
• Remove Drone spec

Ref https://github.com/rancherlabs/eio/issues/2165 for the migration of associated secrets

See https://hub.docker.com/r/rancher/kube-api-auth/tags
for where the images live on Docker Hub.

---

The publication flow (release.yml) was tested with PR #25.
The flow added here differs only in the trigger condition.
The test flow triggered on push_request whereas this here triggers on published release.

The action logs of the test run are at https://github.com/rancher/kube-api-auth/actions/runs/8738114342

The resulting image is at https://hub.docker.com/layers/rancher/kube-api-auth/pr-25/images/sha256-9f13ef730a7683a7eb91f1258d0129d5000a43c762605e234aa142d8f2a6d2fc
Its tag is pr-25, which was automatically chosen by the docker/metadata-action@v5, and is hopefully different enough to not be mistaken for a released version.

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[enrichman]

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