Add option to use Docker container to run Asynqmon

Dockerfile

@@ -0,0 +1,58 @@
+#
+# First stage: 
+# Building a frontend.
+#
+
+FROM alpine:3.13 AS frontend
+
+# Move to a working directory (/static).
+WORKDIR /static
+
+# Install npm (with latest nodejs) and yarn (globally, in silent mode).
+RUN apk add --no-cache npm && \
+    npm i -g -s --unsafe-perm yarn
+
+# Copy only ./ui folder to the working directory.
+COPY ui .
+
+# Run yarn scripts (install & build).
+RUN yarn install && yarn build
+
+#
+# Second stage: 
+# Building a backend.
+#
+
+FROM golang:1.16-alpine AS backend
+
+# Move to a working directory (/build).
+WORKDIR /build
+
+# Copy and download dependencies.
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy a source code to the container.
+COPY . .
+
+# Copy frontend static files from /static to the root folder of the backend container.
+COPY --from=frontend ["/static/build", "/ui/build"]
+
+# Set necessary environmet variables needed for the image and build the server.
+ENV CGO_ENABLED=0 GOOS=linux GOARCH=amd64
+
+# Run go build (with ldflags to reduce binary size).
+RUN go build -ldflags="-s -w" -o asynqmon .
+
+#
+# Third stage: 
+# Creating and running a new scratch container with the backend binary.
+#
+
+FROM scratch
+
+# Copy binary from /build to the root folder of the scratch container.
+COPY --from=backend ["/build/asynqmon", "/"]
+
+# Command to run when starting the container.
+ENTRYPOINT ["/asynqmon"]