Enhance the installer to detect missing composer binary or to add the composer as a real path in Cacti's path setting

[TheWitness]

Feature Request

Is your feature request related to a problem? Please describe

Starting in Cacti 1.3, we require composer. For Windows specifically, we need to know the path of composer and detect it's ability to run as the installer.

Describe the solution you'd like

1. Add a path setting for composer
2. Detect if the <base_path>/include/vendor is writable
3. Run the composer update as install time if writable, or provide instructions for users to first run it if the directory is not writable before proceeding.

Describe alternatives you've considered

There are not many other solutions here.

Additional context

We agreed to this at our monthly developers meeting.