fix: make devcontainer standalone for rust toolchain version (#1411)

.devcontainer/Dockerfile

@@ -11,13 +11,14 @@ RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
 
 RUN apt install -y gh libgmp3-dev
 
-COPY rust-toolchain.toml .
+# To allow independent workflow of the container, the rust-toolchain is explicitely given.
+RUN echo "1.74.0" > rust_toolchain_version
 
 # Install cargo-binstall
 RUN curl -L --proto '=https' --tlsv1.2 -sSf https://raw.githubusercontent.com/cargo-bins/cargo-binstall/main/install-from-binstall-release.sh | bash
 
-RUN rustup toolchain install $(cat rust-toolchain.toml | grep channel | cut -d\" -f2) && \
-    rustup default $(cat rust-toolchain.toml | grep channel | cut -d\" -f2) && \
+RUN rustup toolchain install $(cat rust_toolchain_version) && \
+    rustup default $(cat rust_toolchain_version) && \
     rustup component add clippy && \
     rustup component add rustfmt
 
@@ -37,14 +38,14 @@ RUN if [ "$TARGETPLATFORM" = "linux/arm64" ] ; then \
     mv hurl-4.1.0-aarch64-unknown-linux-gnu/hurl /usr/local/bin/ && \
     rm -r hurl-4.1.0-aarch64-unknown-linux-gnu && \
     rm hurl.tar.gz && \
-    rustup component add llvm-tools-preview --toolchain 1.70.0-aarch64-unknown-linux-gnu; \
+    rustup component add llvm-tools-preview --toolchain $(cat rust_toolchain_version)-aarch64-unknown-linux-gnu; \
     elif [ "$TARGETPLATFORM" = "linux/amd64" ] ; then \
     curl -L https://github.com/Orange-OpenSource/hurl/releases/download/4.1.0/hurl-4.1.0-x86_64-unknown-linux-gnu.tar.gz -o hurl.tar.gz && \
     tar -xzf hurl.tar.gz && \
     mv hurl-4.1.0-x86_64-unknown-linux-gnu/hurl /usr/local/bin/ && \
     rm -r hurl-4.1.0-x86_64-unknown-linux-gnu && \
     rm hurl.tar.gz && \
-    rustup component add llvm-tools-preview --toolchain 1.70.0-x86_64-unknown-linux-gnu && \
+    rustup component add llvm-tools-preview --toolchain $(cat rust_toolchain_version)-x86_64-unknown-linux-gnu && \
     rustup target add x86_64-fortanix-unknown-sgx --toolchain nightly; \
     fi