[CORL-127] Custom CSS (#2194)

* feat: moved html-webpack-plugin to custom server templates in production

* fix: fixed templates

* fix: removed sri for the time being

* fix: fixed up tests for new field name

src/core/client/admin/test/fixtures.ts

@@ -17,7 +17,7 @@ export const settings = {
   closedTimeout: 604800,
   autoCloseStream: false,
   closedMessage: null,
-  customCssUrl: null,
+  customCSSURL: null,
   domains: ["localhost:8080"],
   editCommentWindowLength: 30000,
   communityGuidelines: {