Fixes: #18184 - Gracefully handle unavailable internet connection on RSS feed dashboard widget if ISOLATED_DEPLOYMENT is set

[bctiemann]

Fixes: #18184

Because the RSS feed widget ("NetBox News") will return an error in an isolated deployment, this change skips adding that widget to the default dashboard if ISOLATED_DEPLOYMENT is set in the configuration.

Note that this matches all extras.RSSFeedWidget type widgets, so any additional RSS feeds we add to DEFAULT_DASHBOARD in the future will also be skipped in this situation.

[bctiemann]

Also note that this filtering behavior only occurs when the dashboard object is first populated from DEFAULT_DASHBOARD, which might occur before the user knows to set ISOLATED_DEPLOYMENT in the config. Maybe we should filter the RSS widget(s) out of the user's already-assigned Dashboard object? That feels invasive and presumptuous however.

[jeremystretch]

This works, but I worry about precluding the use of RSS feed widgets entirely for an isolated deployment: It would be valid (though admittedly rare) to want to include an RSS feed from another locally-accessible system.

Maybe we could add a configuration parameter on RSSFeedWidget to indicate whether external access is required. If so, and ISOLATED_DEPLOYMENT is true, the widget will not be displayed. But maybe I'm overthinking it.

[bctiemann]

How would it be if we showed a message like this? It's an error like the regular generic one, but at least the user will know exactly why and what to do about it: