Add docker alpine image

Dockerfile.alpine

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+# Builder image
+FROM golang:1.17.1-alpine AS build
+ENV GOPATH /go
+WORKDIR /go/src/headscale
+
+COPY go.mod go.sum /go/src/headscale/
+RUN apk add gcc musl-dev
+RUN go mod download
+
+COPY . .
+
+RUN go install -a -ldflags="-extldflags=-static" -tags netgo,sqlite_omit_load_extension ./cmd/headscale
+RUN test -e /go/bin/headscale
+
+# Production image
+FROM alpine:latest
+
+COPY --from=build /go/bin/headscale /bin/headscale
+ENV TZ UTC
+
+EXPOSE 8080/tcp
+CMD ["headscale"]