Tools: Disable Python constraint files with environment variable

Constraint files can be disabled with environment variable as well which
is useful when one uses the install/export scripts instead of
idf_tools.py directly. This is option is useful for offline build as
well.

Closes https://github.com/espressif/esp-idf/issues/9263

tools/docker/Dockerfile

@@ -75,6 +75,10 @@ RUN : \
   && rm -rf $IDF_TOOLS_PATH/dist \
   && :
 
+# The constraint file has been downloaded and the right Python package versions installed. No need to check and
+# download this at every invocation of the container.
+ENV IDF_PYTHON_CHECK_CONSTRAINTS=no
+
 # Ccache is installed, enable it by default
 ENV IDF_CCACHE_ENABLE=1
 COPY entrypoint.sh /opt/esp/entrypoint.sh