feat: multi-stage build for container image

Adapt the Makefile and Dockerfile for a multi-stage build of the
container image. It is now not anymore required to have go locally
installed to build the container image.

Inside the multi-stage build, the newly create make install command will
be executed. The compbiled files will than be copied to a new base image
with less dependencies.

Further improvement would be to use instead of debian:10 scratch,
because the application does not have any C dependencies
(CGO_ENABLED=0).

Additionally it is not possible to build the container image with
alternative container runtimes like podman instead of docker.

make build/container-image CONTAINER_RUNTIME=podman

The used base image names are now defined as fully qualified image names
(with registry host), to support local container registry mirror
configurations.

Dockerfile

@@ -1,10 +1,19 @@
-FROM debian:buster-slim
+FROM docker.io/library/golang:1.20.5-buster AS build
 
-# Create main app folder to run from
-WORKDIR /app
+WORKDIR /workspace
+ADD . /workspace
 
-# Copy compiled binary to release image
-# (must build the binary before running docker build)
-COPY fail2ban_exporter /app/fail2ban_exporter
+RUN apt update --yes && \
+    apt install --yes build-essential && \
+    make install \
+      PREFIX=/usr \
+      DESTDIR=/app \
+      EXECUTABLE=fail2ban_exporter
 
-ENTRYPOINT ["/app/fail2ban_exporter"]
+FROM docker.io/library/debian:10-slim
+
+COPY --from=build /app /
+
+EXPOSE 9191
+
+ENTRYPOINT [ "/usr/bin/fail2ban_exporter" ]