Replace amavis with rmilter plus clamav and rspamd

rspamd/Dockerfile

@@ -0,0 +1,10 @@
+FROM alpine:edge
+
+RUN echo "@testing http://nl.alpinelinux.org/alpine/edge/testing" >> /etc/apk/repositories \
+ && apk add --update \
+     rspamd@testing rsyslog \
+ && rm -rf /var/cache/apk/*
+ 
+RUN mkdir /run/rspamd
+
+CMD ["rspamd", "-f", "-i"]