[PWA] Progressive Web App for Joomla: app.webmanifest, sw.js, offline.html & web-app-origin-association

[universewrld]

Pull Request for Issue #44172, #19877, #44171 & #44311

Summary of Changes

4 new files:
app.webmanifest (Manifest for PWA)
sw.js (Service Worker for PWA)
offline.html (Offline Page for PWA)
/.well-known/web-app-origin-association (scope_extensions for PWA)

1 new settings page for PWA in Control Panel
System -> Global Configuration -> PWA

^ this settings page is still not created and I hope you will add this settings page to Joomla.

Such fields for PWA as name and short name by default can be used from the Site settings page from the Site name field, and the description from the Site Meta Description field with the ability to specify your custom text instead of the text from the Site settings tab.

for such PWA fields as icons, shortcuts and screenshots there should be an option to select images from the built-in Media manager, or the ability to specify a custom URL for image.

for such fields as shortcuts there should be an option to select a link from the built-in Joomla link manager (articles, menu items, categories, etc), or the ability to specify a custom URL for link.

Testing Instructions

copy example files app.webmanifest, sw.js, offline.html & web-app-origin-association from #19877 & #44171, replacing the appropriate values with the field values for your website.

you can test your PWA application here: https://www.pwabuilder.com (@pwa-builder test from @microsoft)

Actual result BEFORE applying this Pull Request

Joomla doesn't support PWA, you can't install your website as an app.

Expected result AFTER applying this Pull Request

The website on Joomla is fully compatible with PWA and is ready for installation on Android, iOS, Windows, MacOS and other operating systems as an application.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:
• Pull Request link for manual.joomla.org:

@GoogleChrome What are Progressive Web Apps? - https://web.dev/articles/what-are-pwas
@w3c: Web Application Manifest - https://www.w3.org/TR/appmanifest/
Web App Manifest - Application Information - https://www.w3.org/TR/manifest-app-info/
Explainer - https://github.com/w3c/manifest/blob/gh-pages/explainer.md
@mdn: Web App Manifest - https://developer.mozilla.org/docs/Web/Manifest
@pwa-builder PWA Docs - https://docs.pwabuilder.com/
@microsoft PWA Docs - https://microsoft.github.io/win-student-devs/#/30DaysOfPWA/README
@Wikipedia Wikipedia - https://en.wikipedia.org/wiki/Progressive_web_app

this is the first test version of PWA for @joomla, I hope you will add the necessary files to this pull request and Joomla CMS based on my examples.