Standarize unbound, prepare for setup inclusion

- Use jinja template for configuration file (start.py)
- Limit access to the Mailu subnet
- Implement health checks

services/unbound/Dockerfile

@@ -0,0 +1,18 @@
+FROM python:3-alpine
+
+RUN apk add --no-cache unbound curl bind-tools \
+  && pip3 install jinja2 \
+  && curl -o /etc/unbound/root.hints https://www.internic.net/domain/named.cache \
+  && chown root:unbound /etc/unbound \
+  && chmod 775 /etc/unbound \
+  && apk del --no-cache curl \
+  && /usr/sbin/unbound-anchor -a /etc/unbound/trusted-key.key | true
+
+COPY start.py /start.py
+COPY unbound.conf /unbound.conf
+
+EXPOSE 53/udp 53/tcp
+
+CMD /start.py
+
+HEALTHCHECK CMD dig @127.0.0.1 || exit 1