build (docker): CARGO_PROFILE_RELEASE_LTO="true"

Improve performances significantly for the generated code. This is a must
have when building for release.

docker/Dockerfile

@@ -28,6 +28,7 @@ COPY . .
 # build duniter
 ARG threads=1
 RUN source ~/.cargo/env && \
+	CARGO_PROFILE_RELEASE_LTO="true" \
 	RUSTFLAGS="-C target-feature=-crt-static" \
 		cargo build --release -j $threads