create user in dockerfile, add start script for container

Dockerfile

@@ -3,9 +3,16 @@ FROM debian:latest
 LABEL Maintainer="Wolfgang Hottgenroth <woho@hottis.de>"
 LABEL ImageName="registry.gitlab.com/wolutator/mosquitto-with-auth"
 
+ARG MOSQ_USER="mosquitto"
+ARG MOSQ_UID="1883"
+ARG MOSQ_GID="1883"
+
 RUN \
   apt update && \
-  apt install -y mariadb-client openssl libwebsockets8 
+  apt install -y mariadb-client openssl libwebsockets8 && \
+  groupadd -r -g $MOSQ_GID $MOSQ_USER && \
+  useradd -m -r -u $MOSQ_UID -g $MOSQ_USER $MOSQ_USER
+
 
 COPY opt/ /opt
 COPY etc/ /opt/etc