Merge #1196: Update docker base

3eec6e8 docker: remove pip from resulting image (3np)
5fa4a51 docker: base from buster to bullseye (3np)

Dockerfile

@@ -1,4 +1,4 @@
-FROM debian:buster-slim
+FROM debian:bullseye-slim
 
 RUN mkdir -p /jm/clientserver
 WORKDIR /jm/clientserver
@@ -6,8 +6,9 @@ WORKDIR /jm/clientserver
 COPY . .
 
 RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates=* curl=* \
-  python3-pip=* \
+  python3-pip=* python3=* \
   && pip3 install 'wheel>=0.35.1' \
   && ./install.sh --docker-install \
+  && apt-get purge -y --autoremove python3-pip \
   && apt-get clean \
   && rm -rf /var/lib/apt/lists/*