Docker fix (#8835)

* Fix server command in Dockerfile

* Ensure invoke is installed into the venv

* Run extra check in docker build step

* Improve documentation

* Intercept ModuleNotFoundError

- Clear error message

* Docs updates

* Add extra check to dev docker build

* Cleanup tasks.py

* Prevent double activation of venv

* Change order of operations

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Co-authored-by: Matthias Mair <code@mjmair.com>

contrib/container/Dockerfile

@@ -171,4 +171,4 @@ WORKDIR ${INVENTREE_HOME}
 ENTRYPOINT ["/bin/ash", "./contrib/container/init.sh"]
 
 # Launch the development server
-CMD ["invoke", "server", "-a", "${INVENTREE_WEB_ADDR}:${INVENTREE_WEB_PORT}"]
+CMD ["invoke", "dev.server", "-a", "${INVENTREE_WEB_ADDR}:${INVENTREE_WEB_PORT}"]