chore(build): build dd-trace-py with release mode by default

Author: taegyunkim

Dockerfile

@@ -22,6 +22,8 @@ RUN curl https://sh.rustup.rs -sSf | \
     sh -s -- --default-toolchain stable -y
 ENV PATH=/root/.cargo/bin:$PATH
 
+ENV DD_COMPILE_MODE="Release"
+
 # Install datadog_lambda and dependencies from local
 COPY . .
 RUN pip install --no-cache-dir . -t ./python/lib/$runtime/site-packages