add initial Dockerfile (#11)

fixes the release action

Dockerfile

@@ -0,0 +1,21 @@
+# Go releaser dockerfile
+FROM alpine as certs
+RUN apk update && apk add ca-certificates
+FROM scratch
+COPY slack-proxy /usr/bin/slack-proxy
+COPY --from=certs /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
+# Some of this borrowed from fortiotel's Dockerfile - would need to use tracing for this to be useful
+# TODO: add tracing?
+ENV OTEL_SERVICE_NAME "slack-proxy"
+# Assumes you added --collector.otlp.enabled=true to your Jaeger deployment
+ENV OTEL_EXPORTER_OTLP_ENDPOINT http://jaeger-collector.istio-system.svc.cluster.local:4317
+EXPOSE 9090
+EXPOSE 8080
+# configmap (dynamic flags)
+VOLUME /etc/slack-proxy
+# data files etc
+VOLUME /var/lib/slack-proxy
+WORKDIR /var/lib/slack-proxy
+ENTRYPOINT ["/usr/bin/slack-proxy"]
+# TODO: Need to pass the token as secret or env
+CMD ["-config-dir", "/etc/slack-proxy"]