[bug/admin] Device configuration variables not updating when templates defines same variable

[pandafy]

Consider the following scenario, where there are two templates as follows:

1. Template: "Access Points"
   • Configuration Variable: {'ssid': 'OpenWISP'}
2. Template: "Wireless Radio"
   • Configuration Variable: {'ssid': 'placeholder'}

How to replicate

1. Create a device object
2. Select the "Wireless Radio" template on a device. The configuration variables are populated, and you see {'ssid': 'placeholder'}. This is correct.
3. Now, select the "Access Points" template. Ensure that it comes after the "Wireless Radio" template.

Expected Result:
You would expect the configuration variables to reflect {'ssid': 'OpenWISP'} because the new template has a different value for ssid.

Actual Result:
The configuration variables still show {'ssid': 'placeholder'}.

Explanation:
The issue occurs due to this JavaScript code:

openwisp-controller/openwisp_controller/config/static/config/js/widget.js

Lines 34 to 38 in 14f96ab

	Object.keys(defaultValues).forEach(function (key) {
	if (!contextValue.hasOwnProperty(key) && !systemContextValue.hasOwnProperty(key)) {
	contextValue[key] = defaultValues[key];
	}
	});

The code only updates the configuration variables if the key is not defined in the System Defined Variables and is not already defined in the Configuration Variables for the device.

In this case, when you change the template, the configuration variables already have {'ssid': 'placeholder'} because it was set by the previous template. Therefore, the code does not update the configuration variable, assuming the user intentionally set it and wants to preserve their custom value.

This behavior was likely implemented to prevent overriding of configuration variables that were intentionally set by the user.

Originally posted by @pandafy in #779 (comment)