fix(pwa) move manifest to the root

It must be served from the same origin, so we need to bypass the CDN we use for
meet.jit.si. See the code comments for the rationale on the workaround.

static/pwa/manifest.json

@@ -1,36 +0,0 @@
-{
-  "android_package_name": "org.jitsi.meet",
-  "prefer_related_applications": true,
-  "related_applications": [
-    {
-      "id": "org.jitsi.meet",
-      "platform": "chromeos_play"
-    }
-  ],
-  "short_name": "Jitsi Meet",
-  "name": "Jitsi Meet",
-  "icons": [
-    {
-      "src": "icons/icon192.png",
-      "type": "image/png",
-      "sizes": "192x192"
-    },
-    {
-      "src": "icons/icon512.png",
-      "type": "image/png",
-      "sizes": "512x512"
-    },
-    {
-      "src": "icons/iconMask.png",
-      "sizes": "512x512",
-      "type": "image/png",
-      "purpose": "maskable"
-    }
-  ],
-  "start_url": "/",
-  "background_color": "#17A0DB",
-  "display": "standalone",
-  "scope": "/",
-  "theme_color": "#17A0DB"
- }
-