Self hosted domain redirect (#756)

* Integration pages from Notion

* Self hosted domain redirect

* Refactor root-redirect middleware and update 404 page layout

- Simplified the `root-redirect.js` middleware by removing the specific route checks, allowing for a more general redirect based on the `self_hosted` feature flag.
- Updated the 404 error page in `[...all].vue` by removing the unnecessary `NuxtLayout` wrapper and replacing `NuxtLink` with a custom `UButton` for navigation, enhancing the overall layout and user experience.

These changes aim to streamline the redirect logic and improve the presentation of the 404 error page.

* Refactor feature flag handling and update middleware

- Updated the condition in `Navbar.vue` to correctly evaluate the feature flags for rendering the AI form builder link.
- Removed the `feature-flags.global.js` middleware as it was no longer needed, streamlining the middleware structure.
- Enhanced the `root-redirect.js` middleware to utilize `h3`'s `sendRedirect` for server-side redirection, improving the redirect logic.
- Modified the `ai-form-builder.vue` page to include the new `root-redirect` middleware, ensuring proper redirection based on feature flags.

These changes aim to improve the handling of feature flags and redirection logic, enhancing the overall application flow.

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Co-authored-by: Julien Nahum <julien@nahum.net>

client/components/global/Navbar.vue

@@ -53,7 +53,7 @@
             </a>
           </template>
           <NuxtLink
-            v-if="($route.name !== 'ai-form-builder' && user === null) && (!useFeatureFlag('self_hosted') || useFeatureFlag('ai_features'))"
+            v-if="($route.name !== 'ai-form-builder' && user === null) && (!useFeatureFlag('self_hosted') && useFeatureFlag('ai_features'))"
             :to="{ name: 'ai-form-builder' }"
             :class="navLinkClasses"
             class="hidden lg:inline"