grafana/toolkit: Add font file loader (#19781)

* add file loader for fonts

* Add public path to resolve fonts correctly

* Do not specify font's output path

* Output fonts to fonts directory

packages/grafana-toolkit/src/config/utils/getPluginId.ts

+import path from 'path';
+
+let PLUGIN_ID: string;
+
+export const getPluginId = () => {
+  if (!PLUGIN_ID) {
+    const pluginJson = require(path.resolve(process.cwd(), 'src/plugin.json'));
+    PLUGIN_ID = pluginJson.id;
+  }
+  return PLUGIN_ID;
+};

packages/grafana-toolkit/src/config/webpack/loaders.ts

 import fs from 'fs';
 import path from 'path';
+import { getPluginId } from '../utils/getPluginId';
 
 const MiniCssExtractPlugin = require('mini-css-extract-plugin');
 
@@ -139,5 +140,14 @@ export const getFileLoaders = () => {
             },
       ],
     },
+    {
+      test: /\.(woff|woff2|eot|ttf|otf)(\?v=\d+\.\d+\.\d+)?$/,
+      loader: 'file-loader',
+      options: {
+        publicPath: `/public/plugins/${getPluginId()}/fonts`,
+        outputPath: 'fonts',
+        name: '[name].[ext]',
+      },
+    },
   ];
 };