Add the ability to run syft from a scratch image.

This change will allow endusers or CI to run syft from a
minimum image which will simplify CI deployment.

Signed-off-by: Toure Dunnon <toure.dunnon@anchore.com>

Dockerfile

@@ -0,0 +1,20 @@
+FROM alpine:latest AS build
+
+# add required ca-certificates for https request.
+RUN apk --no-cache add ca-certificates
+
+# create empty directory for scratch image cache.
+RUN mkdir -p /tmp-syft
+
+# reduce container image to scratch size.
+FROM scratch
+
+# Copy directories and files needed to execute syft.
+COPY --from=build /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt
+COPY --from=build /tmp-syft /tmp
+
+# copy syft binary to rootfs
+COPY syft /
+
+# default path
+ENTRYPOINT ["/syft"]