Fix docker container setup for goreleaser

The expected approach is that the binary built by goreleaser is added to
the docker container.

.goreleaser.yml

@@ -102,6 +102,7 @@ dockers:
       - restic/rest-server:{{ .Version }}
     build_flag_templates:
       - "--pull"
+    dockerfile: "Dockerfile.goreleaser"
     extra_files:
       - docker/create_user
       - docker/delete_user

Dockerfile.goreleaser

@@ -0,0 +1,16 @@
+FROM alpine
+
+ENV DATA_DIRECTORY /data
+ENV PASSWORD_FILE /data/.htpasswd
+
+RUN apk add --no-cache --update apache2-utils
+
+COPY docker/create_user /usr/bin/
+COPY docker/delete_user /usr/bin/
+COPY docker/entrypoint.sh /entrypoint.sh
+COPY rest-server /usr/bin
+
+VOLUME /data
+EXPOSE 8000
+
+CMD [ "/entrypoint.sh" ]