Add .dockerignore and adjust Dockerfile

.dockerignore

@@ -0,0 +1,5 @@
+*.log
+output.*.txt
+.vscode
+files
+files.*/

Dockerfile

@@ -1,11 +1,19 @@
+ARG bin_name=docgrouper
+
 FROM golang:1.22 as builder
-WORKDIR /go/src/docgrouper
-COPY testdata testdata/
-COPY *.go go.mod go.sum ./
+ARG bin_name
+WORKDIR /go/src/$bin_name
+COPY . .
 RUN go mod download
-RUN go test -v ./... && CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o docgroup
+RUN go test -v ./... && CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o $bin_name
 
 FROM gcr.io/distroless/base-nossl-debian12
-COPY --from=builder /go/src/docgrouper/docgrouper /bin/docgrouper
+ARG bin_name
+COPY --from=builder /go/src/${bin_name}/${bin_name} /bin/${bin_name}
 VOLUME [ "/files" ]
-ENTRYPOINT [ "docgroup" ]
+
+# ARGs are stupid and cannot be used in ENTRYPOINT, so we still have to
+# hard-code the binary name here, but this is still better than having to
+# hard-code it in the stages above, since it doesn't really matter much what the
+# entrypoint is called.
+ENTRYPOINT [ "docgrouper" ]