Fix Dockerfile permission issues

On docker build after changes from:
kausaltech#46
and
kausaltech#47
there is a build error still:
```
$ podman-compose  -f docker-compose.dev.yml  -f docker-compose.yml --podman-build-args="--security-opt label=disable" up --build --build-arg INSTALL_DEV_DEPS=0 --build-arg BUILD_ID=0
...
Execution of msgfmt failed: msgfmt: error while opening "/venv/lib/python3.12/site-packages/django_filters/locale/fi/LC_MESSAGES/django.mo" for writing: Permission denied
...
CommandError: compilemessages generated one or more errors.
```

The change fixes permission errors by adding required dirs to `chown -R`
call.

After this build finally succeeds.

Note that I ran `podman-compose` because Fedora comes with `podman`, not
`docker`, yet here the behavior of `podman` and `docker` are identical.

docker/app/Dockerfile

@@ -109,7 +109,7 @@ ENV MEDIA_ROOT=${MEDIA_ROOT}
 RUN mkdir -p ${MEDIA_ROOT} ${STATIC_ROOT}
 
 RUN groupadd -g ${app_user_gid} user && useradd --no-log-init -m -d /home/user -g ${app_user_gid} -u ${app_user_uid} -r user
-RUN chown -R user:user /code /srv/media /srv/static
+RUN chown -R user:user /code /locale /venv /srv/media /srv/static
 
 # Switch to the app user
 USER user