Pip-compile may not exist on the installer machine causing script to fail

[erbkaiser]

Describe the bug
The non-dev install instructions do not instruct the user to install pip-tools, or this is not included in the provided scripts, which means that the install fails at the "inv install" step since pip-compile may not be present on the installer machine.

To Reproduce
Steps to reproduce the behaviour:

1. Get a system where Python is not yet installed
2. Follow the non-dev installation instructions exactly until the step 'inv install'
3. Notice the error:
   (.venv) PS C:\Users<username>\Downloads\galaxy-integration-steam-master> inv install
   --> Flattening dependencies to temporary requirements file
   'pip-compile' is not recognized as an internal or external command,
   operable program or batch file.

Expected behavior
pip-compile should be present.

Suggested fix
Add an installer for pip-tools in the script