Add dockerfile for running in docker

Dockerfile

@@ -0,0 +1,27 @@
+FROM golang:1.21-alpine AS builder
+
+WORKDIR /app
+
+RUN apk add --no-cache git
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN go build -o proxmox-cloud-image
+
+FROM ubuntu:22.04
+
+RUN apt-get update && \
+    apt-get install -y \
+    qemu-utils \
+    libguestfs-tools \
+    openssh-client \
+    ca-certificates && \
+    rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /app/proxmox-cloud-image /usr/local/bin/
+
+WORKDIR /workspace
+
+ENTRYPOINT ["proxmox-cloud-image"]