fix(docker): set SHELL to an existing binary

[michaelbeaumont]

Without this command, anything that uses the "default shell" of the image, which is ["/bin/sh", "-c"] will fail because this binary doesn't exist in images derived from this Dockerfile.

For example, if another Dockerfile FROMs these images and it uses the "shell form" of commands as described above, the image will be broken:

diff --git i/tools/releases/dockerfiles/Dockerfile.kuma-cp w/tools/releases/dockerfiles/Dockerfile.kuma-cp
index c6f1a6ce6..27893776a 100644
--- i/tools/releases/dockerfiles/Dockerfile.kuma-cp
+++ w/tools/releases/dockerfiles/Dockerfile.kuma-cp
@@ -3,4 +3,4 @@ FROM kumahq/static-debian11:no-push
 ARG ARCH
 COPY /build/artifacts-linux-$ARCH/kuma-cp/kuma-cp /usr/bin

-ENTRYPOINT ["kuma-cp"]
+ENTRYPOINT kuma-cp run

without SHELL:

❯ docker run docker.io/kumahq/kuma-cp:0.0.0-preview.vlocal-build
docker: Error response from daemon: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: exec: "/bin/sh": stat /bin/sh: no such file or directory: unknown.
ERRO[0000] error waiting for container:

with SHELL:

❯ docker run docker.io/kumahq/kuma-cp:0.0.0-preview.vlocal-build
2023-03-02T14:17:02.463Z	INFO	Skipping reading config from file

Checklist prior to review

• Link to relevant issue as well as docs and UI issues -- feat: consistent docker images #5343
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

[lahabana]

Backport to 2.1?

[michaelbeaumont]

@Mergifyio backport release-2.1

[mergify]

backport release-2.1

✅ Backports have been created

• #6193 fix(docker): set SHELL to an existing binary (backport #6192) has been created for branch release-2.1