strip buildtime dependencies from docker image

Dockerfile

@@ -53,17 +53,21 @@ EXPOSE 8000
 
 COPY api ./
 RUN set -ex; \
-  # install libs
+  # building hiredis
+  BUILD_DEPS="${BUILD_DEPS:-} gcc libc6-dev"; \
+  \
+  # install dependencies
   export DEBIAN_FRONTEND=noninteractive; \
   apt-get update; apt-get install --yes --no-install-recommends \
     libmagic1 \
-    # need to build hiredis
-    gcc \
-    libc-dev \
+    ${BUILD_DEPS:-} \
   ; rm -rf /var/lib/apt/lists/*; \
   \
   # install ovdashboard_api
-  python3 -m pip --no-cache-dir install ./
+  python3 -m pip --no-cache-dir install ./; \
+  \
+  # remove buildtime dependencies
+  apt-get autoremove --yes --purge ${BUILD_DEPS:-};
 
 # add prepared ovdashboard_ui
 COPY --from=build-ui /tmp/ovdashboard_ui /usr/local/share/ovdashboard_ui