cherry-pick: 4326 improve dockerfile

Updates #4326.

* commit 'f987c2559825923b22e910d01c2d42fb06231acc':
  scripts: imp docs; upd alpine
  Simplify Dockerfile Alpine Linux apk usage

scripts/make/Dockerfile

@@ -1,6 +1,6 @@
 # A docker file for scripts/make/build-docker.sh.
 
-FROM alpine:3.13
+FROM alpine:3.16
 
 ARG BUILD_DATE
 ARG VERSION
@@ -21,8 +21,7 @@ LABEL\
 	org.opencontainers.image.version=$VERSION
 
 # Update certificates.
-RUN apk --no-cache --update add ca-certificates libcap tzdata && \
-	rm -rf /var/cache/apk/* && \
+RUN apk --no-cache add ca-certificates libcap tzdata && \
 	mkdir -p /opt/adguardhome/conf /opt/adguardhome/work && \
 	chown -R nobody: /opt/adguardhome
 

scripts/make/build-docker.sh

@@ -50,6 +50,11 @@ readonly docker_image_name
 
 # Set DOCKER_OUTPUT to 'type=image,name=adguard/adguard-home,push=true' if you
 # want (and are allowed) to push to DockerHub.
+#
+# If you want to inspect the resulting image using commands like "docker image
+# ls", change type to docker and also set docker_platforms to a single platform.
+#
+# See https://github.com/docker/buildx/issues/166.
 docker_output="${DOCKER_OUTPUT:-type=image,name=${docker_image_name},push=false}"
 readonly docker_output