help-beta: Add support for displaying font-awesome icons.

In our app, we use the font-awesome stylesheet, add it to our webpack
bundle and use the appropriate class with the <i> tag.
Here. although for font-awesome, we can use the stylesheet to do the
same, we would need to use `webfonts-loader` for our custom icons.
In this astro project, we want to follow the Astro way, and
unplugin-icons fits better with the Astro way of doing things.
See this topic on the discussion on how we chose unplugin-icons:
https://chat.zulip.org/#narrow/channel/19-documentation/topic/Stage.202.3A.20Icons/near/2168842

help-beta/astro.config.mjs

@@ -1,9 +1,22 @@
 import starlight from "@astrojs/starlight";
 import {defineConfig} from "astro/config";
+import Icons from "unplugin-icons/vite";
 
 // https://astro.build/config
 export default defineConfig({
     base: "help-beta",
+    vite: {
+        plugins: [
+            // eslint-disable-next-line new-cap
+            Icons({
+                compiler: "astro",
+                // Icons had a default scale of 1.2, which was making
+                // them look larger than the text around them.
+                scale: 1,
+                defaultStyle: "display: inline; vertical-align: text-bottom;",
+            }),
+        ],
+    },
     integrations: [
         starlight({
             title: "Zulip help center",

help-beta/package.json

@@ -12,11 +12,13 @@
   "dependencies": {
     "@astrojs/check": "^0.9.3",
     "@astrojs/starlight": "^0.34.2",
+    "@iconify-json/fa": "^1.2.1",
     "@types/hast": "^3.0.4",
     "astro": "^5.1.2",
     "hast-util-from-html": "^2.0.3",
     "hast-util-to-html": "^9.0.5",
     "sharp": "^0.34.1",
-    "typescript": "^5.4.5"
+    "typescript": "^5.4.5",
+    "unplugin-icons": "^22.1.0"
   }
 }