toolbx: Nicer CLI packaging.

Add the runas script, make, entr and netbase. Make it more useful as a
base image for packaging CLIs.

toolbx/Dockerfile

 FROM docker.io/debian:testing-backports
 SHELL ["/bin/bash", "-o", "pipefail", "-xc"]
+ADD [ "https://www.shore.co.il/blog/static/runas", "/usr/local/sbin/runas" ]
 # hadolint ignore=DL3008
 RUN rm /etc/apt/apt.conf.d/docker-* && \
     apt-get update && \
     DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
         ca-certificates \
         curl \
+        entr \
         gnupg \
+        gosu \
         libnss-myhostname \
+        make \
+        netbase \
     && \
     export GNUPGHOME=/tmp/gnupghome && \
     mkdir --mode=0700 "$GNUPGHOME" && \
@@ -26,6 +31,7 @@ RUN rm /etc/apt/apt.conf.d/docker-* && \
     #mkdir /etc/krb5.conf.d && \
     echo 'VARIANT_ID=container' >> /etc/os-release && \
     touch /etc/localtime && \
+    chmod 755 /usr/local/sbin/runas && \
     rm -rf /tmp/* /var/tmp/* /var/lib/apt/lists/* /var/cache/apt/archives/*
 COPY --chown=root:root sources.d/* /etc/apt/sources.list.d/
 COPY --chown=root:root preferences.d/* /etc/apt/preferences.d/