Use Sendico SMTP mailbox for local notifications (#57)

infra/images/backend.Dockerfile

@@ -5,7 +5,7 @@ RUN apk add --no-cache protobuf protobuf-dev make
 WORKDIR /src
 COPY Makefile ./
 COPY backend ./backend
-RUN make generate-notifications
+RUN --mount=type=cache,target=/root/.cache/go-build --mount=type=cache,target=/go/pkg/mod make generate-notifications
 ARG MODULE
 WORKDIR /src/backend/${MODULE}
 RUN --mount=type=cache,target=/root/.cache/go-build --mount=type=cache,target=/go/pkg/mod CGO_ENABLED=0 go build -trimpath -o /out/service .