Speed up licenses.txt build during development, add additionalModules (#12510)

- Emit static string for licenses.txt during development for faster builds
- Manually add @primer/octicons to licenses.txt because it's never
  directy imported.

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

package.json

@@ -11,6 +11,7 @@
     "@babel/runtime": "7.11.2",
     "@claviska/jquery-minicolors": "2.3.5",
     "@primer/octicons": "10.0.0",
+    "add-asset-webpack-plugin": "1.0.0",
     "babel-loader": "8.1.0",
     "clipboard": "2.0.6",
     "core-js": "3.6.5",