set default command; add label "podman-run-x11" (for `podman container runlabel`, tested with xephyr)

https://git.hammerle.me/fphammerle/prusa-slicer-container-image/commit/c46c645a65c453269320053a22778fb7ef71d452

Containerfile

@@ -5,3 +5,8 @@ RUN apk add --no-cache \
     anki=24.06.2-r0
 # TODO merge
 RUN apk add --no-cache ttf-dejavu
+
+CMD ["anki"]
+
+# uid & gid in `--user` arbitrary.
+LABEL podman-run-x11="podman run --name anki --rm --user 25772:34044 --env HOME=/mnt/home --env DISPLAY --env QTWEBENGINE_DISABLE_SANDBOX=1 --read-only --read-only-tmpfs=false --volume anki_share:/mnt/home/.local/share/Anki2/ --tmpfs /tmp:size=1M --volume /tmp/.X11-unix/:/tmp/.X11-unix/ --cap-drop ALL --security-opt no-new-privileges \${IMAGE}"