Make a statically linked build

[eternal-flame-AD]

Currently none of the official builds will work on Alpine, we should have a statically linked build. sqlite3 is public domain so I don't think there should be non-technical complications, something like this (and changing the server build script to append not overwrite LD_FLAGS) should work.

ARG GO_VERSION
FROM gotify/build:$GO_VERSION-linux-amd64
ARG VCS_REF
RUN \
  apt-get update && \
  apt-get install -y musl-tools

ENV CGO_ENABLED=1
ENV GOOS=linux
ENV GOARCH=amd64
ENV LD_FLAGS="-linkmode external -extldflags '-static'"
ENV CC=musl-gcc

LABEL org.opencontainers.image.source="https://github.com/gotify/build" \
  org.opencontainers.image.revision=$VCS_REF 

However since there are no system libc dependencies here or plugin compatibility issues (it's not a dynamically linked system so no plugins), another options is to simply don't use docker at all and build a strictly statically linked binary straight from GH Actions, but out of consistency I think going with docker is good.

[jmattheis]

Yeah, I'm okay with this, but gotify/server must output a user friendly error message when the user attempts to load plugins.

[eternal-flame-AD]

@jmattheis Yes, we can document plugins won't work on static builds first.

I was thinking about maybe redirecting most casual use of plugins (message/API wrangling) into IPC or embedded languages (gojq, etc), and reserve binary plugins for people who really wants to do their custom builds, but I will open an RFC once I have a more concrete plan.