Remove environments from Dockerfile

[npepinpe]

Description

Once we have Kubernetes 1.23+ in all the stages, it would be great to simplify our Dockerfile and remove the APP_ENV usage. We won't really need the development version of the image anymore since we will have access to ephemeral containers, letting us attach an image with all our utilities as a sidecar container of our production image.

[menski]

Once we have Kubernetes 1.23+ in all the stages
Might not be needed for SaaS as we don't have the dev image there

We would only need to wait for our zeebe-io cluster. Until then we need this as a way to have the dev container available.

[megglos]

@npepinpe how should we best inform the whole team about this change or is everyone already familiar with ephemeral container usage?
Currently checking https://iximiuz.com/en/posts/kubernetes-ephemeral-containers myself.

[npepinpe]

I could do a short intro to ephemeral containers. I don't think there's enough to make a full techtalk (e.g. 1h of contents), but if there's no topic we could use that slot for a presentation.

[npepinpe]

I think anyway only Chris uses the dev image, so at the moment he would be the only one impacted

[npepinpe]

Of course, as you're doing this, you could also consider doing the intro to ephemeral containers yourself if you'd like :)

[megglos]

With the changes I tried debugging via ephemeral containers on a benchmark.

kubectl -n <ns> debug -it -c debugger --image=eclipse-temurin:17-jdk-focal --target=zeebe <pod>

which resulted in

Targeting container "zeebe". If you don't see processes from this container it may be because the container runtime doesn't support this feature.
If you don't see a command prompt, try pressing enter.
root@meg-10104-ephemeral-benchmark-zeebe-0:/# ps x
    PID TTY      STAT   TIME COMMAND
      1 ?        Ss     0:00 tini -- /usr/local/bin/startup.sh
      7 ?        Sl     4:48 /opt/java/openjdk/bin/java -Xms128m -XX:+ExitOnOutOfMemoryError -Dfile.encoding=UTF-8 -classpath /usr/local/zeebe/config:/usr/local/zeebe/lib/* -Dapp.name=b
    178 pts/0    Ss     0:00 bash
    187 pts/0    R+     0:00 ps x

The filesystem of the zeebe process can be accessed via the proc folder:

cd /proc/<pid>/root