No feedback on Containerfile directives that do not work with bootc

I don't know how to solve this, but there's a whole bunch of Containerfile commands that do not work or work differently with bootc containers. As a user, I don't see a warning at build or runtime about these:

* EXPOSE: Has no effect.
* ENTRYPOINT: ```/sbin/init``` should be the ```CMD``` ... and the usual ```CMD``` related to the workload needs to become a systemd service or quadlet?
* STOPSIGNAL: Seems this always needs to be SIGRTMIN+3?
* WORKDIR: When used to place executables or files accessed by a systemd service, fails due to SELinux behaving differently with a container than with a booted host. See #439

Others?

* ENV: Has an effect at buildtime, does it work at runtime?
* HEALTHCHECK
* SHELL
* VOLUME

Again, Not sure how these would work. but the user is seems to be expected to discover these differences.

Empieza por inventariar las directivas de Containerfile enumeradas y las diferencias descritas para bootc durante la compilación y en tiempo de ejecución. Lee la discusión relacionada en #439 y determina después si cada directiva necesita una advertencia, documentación o ambas; done debe identificar claramente el comportamiento compatible y los comentarios visibles para el usuario en cada caso.

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