Deb: add Bullseye support

builder/dockerfile.debian_bullseye.deb.build

@@ -0,0 +1,12 @@
+FROM debian:bullseye
+
+ENV DEBIAN_FRONTEND noninteractive
+
+RUN apt-get update && \
+      apt-get -y install vim build-essential devscripts equivs
+
+# Install build-deps for the package.
+COPY ./debian/control /tmp
+RUN echo YYY | mk-build-deps --install --remove /tmp/control
+
+USER 1000