update promtail base image to debian:bullseye-slim

clients/cmd/promtail/Dockerfile

@@ -1,23 +1,23 @@
-FROM golang:1.17.2-buster as build
+FROM golang:1.17.2-bullseye as build
 # TOUCH_PROTOS signifies if we should touch the compiled proto files and thus not regenerate them.
 # This is helpful when file system timestamps can't be trusted with make
 ARG TOUCH_PROTOS
 COPY . /src/loki
 WORKDIR /src/loki
 # Backports repo required to get a libsystemd version 246 or newer which is required to handle journal +ZSTD compression
-RUN echo "deb http://deb.debian.org/debian buster-backports main" >> /etc/apt/sources.list
-RUN apt-get update && apt-get install -t buster-backports -qy libsystemd-dev
+RUN echo "deb http://deb.debian.org/debian bullseye-backports main" >> /etc/apt/sources.list
+RUN apt-get update && apt-get install -t bullseye-backports -qy libsystemd-dev
 RUN make clean && (if [ "${TOUCH_PROTOS}" ]; then make touch-protos; fi) && make BUILD_IN_CONTAINER=false promtail
 
 # Promtail requires debian as the base image to support systemd journal reading
-FROM debian:buster-slim
+FROM debian:bullseye-slim
 # tzdata required for the timestamp stage to work
 # Backports repo required to get a libsystemd version 246 or newer which is required to handle journal +ZSTD compression
-RUN echo "deb http://deb.debian.org/debian buster-backports main" >> /etc/apt/sources.list
+RUN echo "deb http://deb.debian.org/debian bullseye-backports main" >> /etc/apt/sources.list
 RUN apt-get update && \
   apt-get install -qy \
   tzdata ca-certificates
-RUN apt-get install -t buster-backports -qy libsystemd-dev && \
+RUN apt-get install -t bullseye-backports -qy libsystemd-dev && \
   rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 COPY --from=build /src/loki/clients/cmd/promtail/promtail /usr/bin/promtail
 COPY clients/cmd/promtail/promtail-docker-config.yaml /etc/promtail/config.yml