Smaller docker image (#12824)

* build: makes the grafana docker image smaller.

* build: branches and PR:s builds the docker image.

packaging/docker/Dockerfile

@@ -1,6 +1,17 @@
 FROM debian:stretch-slim
 
 ARG GRAFANA_TGZ="grafana-latest.linux-x64.tar.gz"
+
+RUN apt-get update && apt-get install -qq -y tar && \
+    apt-get autoremove -y && \
+    rm -rf /var/lib/apt/lists/*
+
+COPY ${GRAFANA_TGZ} /tmp/grafana.tar.gz
+
+RUN mkdir /tmp/grafana && tar xfvz /tmp/grafana.tar.gz --strip-components=1 -C /tmp/grafana
+
+FROM debian:stretch-slim
+
 ARG GF_UID="472"
 ARG GF_GID="472"
 
@@ -12,15 +23,13 @@ ENV PATH=/usr/share/grafana/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bi
     GF_PATHS_PLUGINS="/var/lib/grafana/plugins" \
     GF_PATHS_PROVISIONING="/etc/grafana/provisioning"
 
-RUN apt-get update && apt-get install -qq -y tar libfontconfig ca-certificates && \
+RUN apt-get update && apt-get install -qq -y libfontconfig ca-certificates && \
     apt-get autoremove -y && \
     rm -rf /var/lib/apt/lists/*
 
-COPY ${GRAFANA_TGZ} /tmp/grafana.tar.gz
+COPY --from=0 /tmp/grafana "$GF_PATHS_HOME"
 
 RUN mkdir -p "$GF_PATHS_HOME/.aws" && \
-    tar xfvz /tmp/grafana.tar.gz --strip-components=1 -C "$GF_PATHS_HOME" && \
-    rm /tmp/grafana.tar.gz && \
     groupadd -r -g $GF_GID grafana && \
     useradd -r -u $GF_UID -g grafana grafana && \
     mkdir -p "$GF_PATHS_PROVISIONING/datasources" \