ci: add Dockerfile and GHCR multi-arch publish workflow

self-hosted/Dockerfile

@@ -0,0 +1,14 @@
+# syntax=docker/dockerfile:1.7
+FROM --platform=$BUILDPLATFORM golang:1.22-alpine AS build
+ARG TARGETOS
+ARG TARGETARCH
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH \
+    go build -trimpath -ldflags="-s -w" -o /out/app .
+
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY --from=build /out/app /app
+ENTRYPOINT ["/app"]