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

---------

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

docs/docs/start/install.md

@@ -107,7 +107,8 @@ source ./env/bin/activate
 The Python packages required by the InvenTree server must be installed into the virtual environment.
 
 ```
-pip install --require-hashes -U -r src/backend/requirements.txt
+pip install --upgrade --ignore-installed invoke
+invoke install
 ```
 
 This installs all required Python packages using pip package manager. It also creates a (default) database configuration file which needs to be edited to meet user needs before proceeding (see next step below).

docs/docs/start/intro.md

@@ -82,6 +82,24 @@ Or, if that does not work, try:
 
 This will place the current shell session inside a virtual environment - the terminal should display the ``(env)`` prefix.
 
+### Invoke in Virtual Environment
+
+If you are using a virtual environment (and you should be!) you will need to ensure that you have installed the `invoke` package inside the virtual environment! If the invoke commands are run from outside the virtual environment, they may not work correctly - and may be extremely difficult to debug!
+
+To install the `invoke` package inside the virtual environment, run the following command (after activating the virtual environment):
+
+```
+pip install --upgrade --ignore-installed invoke
+```
+
+To check that the `invoke` package is correctly installed, run the following command:
+
+```
+which invoke
+```
+
+This should return the path to the `invoke` binary inside the virtual environment. If the path is *not* inside the virtual environment, the `invoke` package is not correctly installed!
+
 ## InvenTree Source Code
 
 InvenTree source code is distributed on [GitHub](https://github.com/inventree/inventree/), and the latest version can be downloaded (using Git) with the following command: