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

## 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