Admin AI settings: Migrate to use PageHeading component

What does this MR do and why?

Migrates page headings to the shared PageHeading component

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. http://gdk.test:3000/admin/code_suggestions
2. http://gdk.test:3000/admin/ai/self_hosted_models

Related to #474921 (closed)

ee/app/assets/javascripts/pages/admin/ai/self_hosted_models/components/app.vue

 <script>
 import { GlEmptyState, GlButton, GlSkeletonLoader } from '@gitlab/ui';
 import EmptyEnvironmentSvg from '@gitlab/svgs/dist/illustrations/empty-state/empty-environment-md.svg?url';
+import PageHeading from '~/vue_shared/components/page_heading.vue';
 import { s__ } from '~/locale';
 import { createAlert } from '~/alert';
 import getSelfHostedModelsQuery from '../graphql/queries/get_self_hosted_models.query.graphql';
@@ -13,6 +14,7 @@ export default {
     GlButton,
     GlSkeletonLoader,
     SelfHostedModelsTable,
+    PageHeading,
   },
   props: {
     basePath: {
@@ -77,23 +79,20 @@ export default {
       </div>
     </div>
     <div v-else>
-      <section>
-        <h1 class="page-title gl-text-size-h-display">
-          {{ s__('AdminSelfHostedModels|Self-hosted models') }}
-        </h1>
-        <div class="gl-items-top gl-flex gl-justify-between gl-pb-2">
-          <p>
-            {{
-              s__('AdminSelfHostedModels|Manage AI models that can be used for GitLab AI features.')
-            }}
-          </p>
-          <div v-if="hasModels" class="gl-pb-4">
-            <gl-button category="primary" variant="confirm" :href="newSelfHostedModelPath"
-              >{{ s__('AdminSelfHostedModels|Add self-hosted model') }}
-            </gl-button>
-          </div>
-        </div>
-      </section>
+      <page-heading :heading="s__('AdminSelfHostedModels|Self-hosted models')">
+        <template #description>
+          {{
+            s__('AdminSelfHostedModels|Manage AI models that can be used for GitLab AI features.')
+          }}
+        </template>
+
+        <template v-if="hasModels" #actions>
+          <gl-button category="primary" variant="confirm" :href="newSelfHostedModelPath"
+            >{{ s__('AdminSelfHostedModels|Add self-hosted model') }}
+          </gl-button>
+        </template>
+      </page-heading>
+
       <gl-skeleton-loader v-if="isLoading" />
       <self-hosted-models-table v-else :models="selfHostedModels" :base-path="basePath" />
     </div>