feat: add signal Docker

Dockerfile

@@ -0,0 +1,19 @@
+FROM docker.io/golang:1.16 AS build
+
+WORKDIR /src
+
+COPY go.mod .
+COPY cmd .
+COPY connection .
+COPY iface .
+COPY signal .
+COPY util .
+COPY main.go .
+
+RUN go mod download
+RUN go mod tidy
+RUN go install .
+
+FROM gcr.io/distroless/base
+COPY --from=build /go/bin/wiretrustee /
+ENTRYPOINT [ "/wiretrustee signal" ]