docker: build empty project with Cargo.toml and Cargo.lock for cache

Dockerfile

@@ -7,6 +7,13 @@ ENV TINI_VERSION v0.19.0
 ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini-static /tini-static
 RUN sudo chmod +x /tini-static
 
+# Copy to Cargo setting and change the owner
+COPY --chown=rust:rust Cargo.toml Cargo.lock ./
+# Build empty project for better cache
+RUN mkdir src && \
+    echo "fn main() {}" > src/main.rs && \
+    cargo build --release && rm -r src
+
 # Copy to current directory and change the owner
 COPY --chown=rust:rust . ./
 # Build