docker: add alpine dockerfile

Dockerfile.alpine

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+# Lightweight Alpine-based pg_featureserv Docker Image
+# Author: jingsam
+FROM golang:1.15.5-alpine3.12
+
+# Build ARGS
+ARG VERSION="latest-alpine-3.12"
+
+RUN mkdir /app
+ADD . /app/
+WORKDIR /app
+RUN go build -v -ldflags "-s -w -X main.programVersion=${VERSION}"
+
+# Multi-stage build: only copy build result and resources
+FROM alpine:3.12
+
+ARG VERSION
+
+LABEL original_developer="Crunchy Data" \
+    contributor="jingsam <[email protected]>" \
+    vendor="Crunchy Data" \
+  url="https://crunchydata.com" \
+  release="${VERSION}" \
+  org.opencontainers.image.vendor="Crunchy Data" \
+  os.version="3.12"
+
+RUN apk --no-cache add ca-certificates
+COPY --from=0 /app/pg_featureserv .
+COPY --from=0 /app/assets ./assets
+
+VOLUME ["/config"]
+VOLUME ["/assets"]
+
+USER 1001
+EXPOSE 9000
+
+ENTRYPOINT ["/pg_featureserv"]
+CMD []
+
+# To build and run specific version
+#
+# export VERSION="latest-alpine-3.12"
+# docker build --build-arg VERSION=${VERSION} -t pramsey/pg_featureserv:${VERSION} -f Dockerfile.alpine
+#
+# Best is to use another PostGIS Docker Container whoose host is reachable from the pg_featureserv Container.
+# docker run -dt -e DATABASE_URL=postgres://user:pass@host/dbname -p 9000:9000 pramsey/pg_featureserv:${VERSION}