docker: add Dockerfile and .dockerignore.

The Dockerfile produces a scratch image with a statically linked binary without debug flag.

Author: nvanheuverzwijn

.dockerignore

@@ -0,0 +1,6 @@
+*
+!go.mod
+!go.sum
+!*.go
+!Makefile
+!internal/*

Dockerfile

@@ -0,0 +1,8 @@
+FROM golang:1.15 AS builder
+WORKDIR /go/src/github.com/adnanh/webhook/
+COPY . ./
+RUN make CGO_ENABLED=0 LDFLAGS="-w -s" build
+
+FROM scratch
+COPY --from=builder /go/src/github.com/adnanh/webhook/webhook /bin/
+ENTRYPOINT ["/bin/webhook"]