Docker: milter daemon, news, docs, github action

The milter default was not set correctly so it was starting
clamav-milter by default. Added default true/false settings for each of
the docker daemon environment variables.

Added command to entrypoint to change database directory ownership to
the clamav user, in case it is a mounted volume (which get root ownership
by default).

Removed the clamav user & group from the build image, as it isn't needed
until the base image.

Added announcement details and acknowledgements to the News document.

Added details to the Docker Readme describing:

- the tag naming convention
- how to mount database volumes
- various other tweaks

Fixed the path for the update script in the GitHub Action, and changed
from alpine-latest to ubuntu-latest, because alpine-latest doesn't seem
to be an option.

.github/workflows/docker-db-update.yml

@@ -0,0 +1,15 @@
+name: Docker image virus database update
+
+on:
+  schedule:
+    - cron: '0 0 1 * *'
+
+jobs:
+  update-image-databases:
+    runs-on: ubuntu-latest
+    env:
+      CLAMAV_DOCKER_USER: ${{ secrets.CLAMAV_DOCKER_USER }}
+      CLAMAV_DOCKER_PASSWD: ${{ secrets.CLAMAV_DOCKER_PASSWD }}
+    steps:
+      - name: Update virus database and push image
+        run: ./dockerfiles/update_db_image.sh

.github/workflows/docker_virusdb-update.yml

@@ -1,16 +0,0 @@
-name: Docker image virus database update
-
-on:
-  schedule:
-    - cron: "0 0 1 * *"
-
-jobs:
-  Release_virusdb_update:
-    runs-on: alpine-latest
-
-    steps:
-      - name: Release update virus database and push image
-        env:
-          CLAMAV_DOCKER_PASSWD: "${{ secrets.CLAMAV_DOCKER_PASSWD }}"
-          CLAMAV_DOCKER_USER: "${{ secrets.CLAMAV_DOCKER_USER }}"
-        run: "dockerfiles/release_db_update.sh"