MM-52536 Webpack unification part 1 (#23322)

* MM-52536 Update Webpack and use the same version for all products

* Switch Channels to use asset modules

* Remove unused module configuration from Boards/Playbooks

* Remove file-loader and html-loader

* Unify versions of CSS-related loaders

* Remove unused webpack-node-externals dependency

* Add missing MiniCssExtractPlugin to Boards/Playbooks production builds

webapp/channels/tsconfig.json

@@ -27,7 +27,6 @@
         "mattermost-redux/*": ["packages/mattermost-redux/src/*"],
         "reselect": ["packages/reselect/src"],
         "@mui/styled-engine": ["./node_modules/@mui/styled-engine-sc"],
-        "!!file-loader*": ["utils/empty-string"],
     }
   },
   "include": [