feature: upgrade Astro to v5 beta (#189)

# Changes

- Upgrade Astro to the version 5 beta

# Associated issue

Resolves #188

# How to test

1. Open preview link
2. See if it works
3. Check code mainly

# Checklist

- [x] I have performed a self-review of my own code
- [x] I have made sure that my PR is easy to review (not too big,
includes comments)
- ~~I have made updated relevant documentation files (in project README,
docs/, etc)~~
- ~~I have added a decision log entry if the change affects the
architecture or changes a significant technology~~
- [x] I have notified a reviewer

<!-- Please strike through and check off all items that do not apply
(rather than removing them) -->

astro.config.ts

@@ -21,30 +21,28 @@ export default defineConfig({
       enabled: true,
     },
   }),
-  experimental: {
-    env: {
-      schema: {
-        DATOCMS_READONLY_API_TOKEN: envField.string({
-          context: 'server',
-          access: 'secret',
-          default: process.env.DATOCMS_READONLY_API_TOKEN
-        }),
-        HEAD_START_PREVIEW_SECRET: envField.string({
-          context: 'server',
-          access: 'secret',
-          default: process.env.HEAD_START_PREVIEW_SECRET
-        }),
-        HEAD_START_PREVIEW: envField.boolean({
-          context: 'server',
-          access: 'secret',
-          default: isPreview
-        }),
-        PUBLIC_IS_PRODUCTION: envField.boolean({
-          context: 'server',
-          access: 'public',
-          default: process.env.NODE_ENV === 'production'
-        })
-      }
+  env: {
+    schema: {
+      DATOCMS_READONLY_API_TOKEN: envField.string({
+        context: 'server',
+        access: 'secret',
+        default: process.env.DATOCMS_READONLY_API_TOKEN
+      }),
+      HEAD_START_PREVIEW_SECRET: envField.string({
+        context: 'server',
+        access: 'secret',
+        default: process.env.HEAD_START_PREVIEW_SECRET
+      }),
+      HEAD_START_PREVIEW: envField.boolean({
+        context: 'server',
+        access: 'secret',
+        default: isPreview
+      }),
+      PUBLIC_IS_PRODUCTION: envField.boolean({
+        context: 'server',
+        access: 'public',
+        default: process.env.NODE_ENV === 'production'
+      })
     }
   },
   image: {
@@ -53,7 +51,7 @@ export default defineConfig({
     service: passthroughImageService()
   },
   integrations: [sitemap()],
-  output: isPreview ? 'server' : 'hybrid',
+  output: isPreview ? 'server' : 'static',
   server: { port: localhostPort },
   site: siteUrl,
   trailingSlash: 'always',