No remote sources in manifest assets

[antonag32]

Is your feature request related to a problem?
Using public CDNs is considered a bad practice. Therefore we should verify that no remote assets are referenced in modules' manifest files. For example, the following snippet in a __manifest__.py is not a good idea:

"assets": {
        "web.assets_frontend": ["https://some.random.cdn/myfile.js"]
}

Important, this only applies to content inside the assets key, as module descriptions may reference websites and that is fine.

Describe the solution you'd like
A new lint that checks for remote URLs inside manifest assets.