added distroless docker file

dev/docker-distroless/Dockerfile

+FROM golang:1 
+WORKDIR /src
+ENV CGO_ENABLED 0
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN go build github.com/bolkedebruin/rdpgw/cmd/rdpgw
+
+FROM gcr.io/distroless/static-debian11:nonroot
+WORKDIR /config
+COPY --from=0 /src/rdpgw /rdpgw
+CMD ["/rdpgw"]
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