set up migrations on deploy

backend/Dockerfile

@@ -44,6 +44,7 @@ WORKDIR /app
 ENV APP_NAME=backend
 
 COPY --from=build /app/_build/prod/rel/${APP_NAME} ./
+COPY Procfile ./
 RUN chown -R nobody: /app
 USER nobody
 

backend/Procfile

@@ -0,0 +1,2 @@
+web: /app/bin/backend start
+release: /app/bin/backend eval "Backend.Release.migrate"