Add Dockerfile for builds with debug symbols enabled. (#479)

build/Dockerfile.dsym

+## Copyright 2018 The Nakama Authors
+##
+## Licensed under the Apache License, Version 2.0 (the "License");
+## you may not use this file except in compliance with the License.
+## You may obtain a copy of the License at
+##
+## http://www.apache.org/licenses/LICENSE-2.0
+##
+## Unless required by applicable law or agreed to in writing, software
+## distributed under the License is distributed on an "AS IS" BASIS,
+## WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+## See the License for the specific language governing permissions and
+## limitations under the License.
+
+# docker build "$PWD" --build-arg commit="$(git rev-parse --short HEAD)" --build-arg version=v2.1.1 -t heroiclabs/nakama:2.1.1
+# docker build "$PWD" --build-arg commit="$(git rev-parse --short HEAD)" --build-arg version="v2.1.1-$(git rev-parse --short HEAD)" -t heroiclabs/nakama-prerelease:"2.1.1-$(git rev-parse --short HEAD)"
+
+FROM golang:1.15.2-buster as builder
+
+ARG commit
+ARG version
+
+ENV GOOS linux
+ENV GOARCH amd64
+ENV CGO_ENABLED 1
+
+RUN apt-get update && \
+    apt-get -y upgrade && \
+    apt-get install -y --no-install-recommends ca-certificates gcc libc6-dev git && \
+    git config --global advice.detachedHead false && \
+    git clone --quiet --no-checkout https://github.com/heroiclabs/nakama /go/build/nakama
+
+WORKDIR /go/build/nakama
+RUN git checkout --quiet "$commit" && \
+    go build -o /go/build-out/nakama -trimpath -mod=vendor -gcflags "all=-N -l" -ldflags "-X main.version=$version -X main.commitID=$commit"
+
+FROM debian:buster-slim
+
+MAINTAINER Heroic Labs <support@heroiclabs.com>
+
+ARG version
+
+LABEL version=$version
+LABEL variant=nakama
+LABEL description="Distributed server for social and realtime games and apps."
+
+RUN mkdir -p /nakama/data/modules && \
+    apt-get update && \
+    apt-get -y upgrade && \
+    apt-get install -y --no-install-recommends ca-certificates=20190110 tzdata curl iproute2 unzip rsync git tini schroot && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/*
+
+WORKDIR /nakama/
+COPY --from=builder "/go/build-out/nakama" /nakama/
+EXPOSE 7349 7350 7351
+
+ENTRYPOINT ["tini", "--", "/nakama/nakama"]
+
+HEALTHCHECK --interval=5m --timeout=10s \
+  CMD curl -f http://localhost:7350/ || exit 1