feat: dockerfile and github based CI build for Africastalking variant (#174)

## Summary

* fixed missing error handler in main
* add injectable build string in main
* add (dynamically linked) docker build
* add github CI workflow
* add extra but useful dev files in dev folder

* closes #93

## Notes

* We'll move to a self-hosted CI runner once it is installed on Gitea.

Reviewed-on: #174
Co-authored-by: Mohammed Sohail <sohailsameja@gmail.com>
Co-committed-by: Mohammed Sohail <sohailsameja@gmail.com>

Dockerfile

@@ -0,0 +1,40 @@
+FROM golang:1.23.0-bookworm AS build
+
+ENV CGO_ENABLED=1
+
+ARG BUILDPLATFORM
+ARG TARGETPLATFORM
+ARG BUILD=dev
+
+WORKDIR /build
+COPY . .
+RUN apt update && apt install libgdbm-dev
+RUN git clone https://git.defalsify.org/vise.git go-vise
+
+WORKDIR /build/services/registration
+RUN echo "Compiling go-vise files"
+RUN make VISE_PATH=/build/go-vise -B
+
+WORKDIR /build
+RUN echo "Building on $BUILDPLATFORM, building for $TARGETPLATFORM"
+RUN go mod download
+RUN go build -o ussd-africastalking -ldflags="-X main.build=${BUILD} -s -w" cmd/africastalking/main.go
+
+FROM debian:bookworm-slim
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN apt update && apt install libgdbm-dev ca-certificates -y
+RUN apt-get clean && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /service
+
+COPY --from=build /build/ussd-africastalking .
+COPY --from=build /build/LICENSE .
+COPY --from=build /build/README.md .
+COPY --from=build /build/services ./services
+COPY --from=build /build/.env .
+
+EXPOSE 7123
+
+CMD ["./ussd-africastalking"]