Dockerize, and switch back to main boringtun repo

Dockerfile

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+FROM rust:1.55 as cargo-build
+RUN apt-get update
+
+WORKDIR /usr/src/onetun
+COPY Cargo.toml Cargo.toml
+
+# Placeholder to download dependencies and cache them using layering
+RUN mkdir src/
+RUN echo "fn main() {println!(\"if you see this, the build broke\")}" > src/main.rs
+RUN cargo build --release
+RUN rm -f target/x86_64-unknown-linux-musl/release/deps/myapp*
+
+# Build the actual project
+COPY . .
+RUN cargo build --release
+
+FROM debian:11-slim
+
+COPY --from=cargo-build /usr/src/onetun/target/release/onetun /usr/local/bin/onetun
+
+# Run as non-root
+RUN chown 1000 /usr/local/bin/onetun
+USER 1000
+
+ENTRYPOINT ["/usr/local/bin/onetun"]