[assets] configurable URL for static resources (#7911)

* static url

* add cors support for static resources

* [assets] work on the migration to configurable url for assets

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

* [misc] fix whitespace

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

* [assets] fix the loading of the manifest.json

It is generated dynamically, and as such can not be served by the cdn.

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

* Revert "add cors support for static resources"

This reverts commit 42f964fd18

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

* [docs] add the STATIC_URL_PREFIX option

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

* [docs] reverse-proxy: nginx: add two setups for STATIC_URL_PREFIX

Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

* [assets] migrate the url of a new asset to the static url prefix

REF: f2a3abc683
Signed-off-by: Jakob Ackermann <das7pad@outlook.com>

templates/pwa/manifest_json.tmpl

@@ -3,22 +3,22 @@
     "name": "Gitea - Git with a cup of tea",
     "icons": [
       {
-        "src": "{{AppSubUrl}}/img/gitea-lg.png",
+        "src": "{{StaticUrlPrefix}}/img/gitea-lg.png",
         "type": "image/png",
         "sizes": "880x880"
       },
       {
-        "src": "{{AppSubUrl}}/img/gitea-sm.png",
+        "src": "{{StaticUrlPrefix}}/img/gitea-sm.png",
         "type": "image/png",
         "sizes": "120x120"
       },
       {
-        "src": "{{AppSubUrl}}/img/gitea-512.png",
+        "src": "{{StaticUrlPrefix}}/img/gitea-512.png",
         "type": "image/png",
         "sizes": "512x512"
       },
       {
-        "src": "{{AppSubUrl}}/img/gitea-192.png",
+        "src": "{{StaticUrlPrefix}}/img/gitea-192.png",
         "type": "image/png",
         "sizes": "192x192"
       }
@@ -28,4 +28,4 @@
     "background_color": "#FAFAFA",
     "display": "standalone",
     "theme_color": "{{ThemeColorMetaTag}}"
-  }
+  }