Update GlLink buttons to GlButtons on Release pages

This commit updates all GlLinks with class="btn" to
GlButtons on any Release-related pages.

app/assets/javascripts/releases/components/app_index.vue

 <script>
 import { mapState, mapActions } from 'vuex';
-import { GlSkeletonLoading, GlEmptyState, GlLink } from '@gitlab/ui';
+import { GlSkeletonLoading, GlEmptyState, GlLink, GlButton } from '@gitlab/ui';
 import {
   getParameterByName,
   historyPushState,
@@ -18,6 +18,7 @@ export default {
     ReleaseBlock,
     TablePagination,
     GlLink,
+    GlButton,
   },
   props: {
     projectId: {
@@ -69,14 +70,16 @@ export default {
 </script>
 <template>
   <div class="flex flex-column mt-2">
-    <gl-link
+    <gl-button
       v-if="newReleasePath"
       :href="newReleasePath"
       :aria-describedby="shouldRenderEmptyState && 'releases-description'"
-      class="btn btn-success align-self-end mb-2 js-new-release-btn"
+      category="primary"
+      variant="success"
+      class="align-self-end mb-2 js-new-release-btn"
     >
       {{ __('New release') }}
-    </gl-link>
+    </gl-button>
 
     <gl-skeleton-loading v-if="isLoading" class="js-loading" />
 

app/assets/javascripts/releases/components/release_block_header.vue

 <script>
-import { GlTooltipDirective, GlLink, GlBadge } from '@gitlab/ui';
+import { GlTooltipDirective, GlLink, GlBadge, GlButton } from '@gitlab/ui';
 import Icon from '~/vue_shared/components/icon.vue';
 import { BACK_URL_PARAM } from '~/releases/constants';
 import { setUrlParams } from '~/lib/utils/url_utility';
@@ -10,6 +10,7 @@ export default {
     GlLink,
     GlBadge,
     Icon,
+    GlButton,
   },
   directives: {
     GlTooltip: GlTooltipDirective,
@@ -50,14 +51,16 @@ export default {
         __('Upcoming Release')
       }}</gl-badge>
     </h2>
-    <gl-link
+    <gl-button
       v-if="editLink"
       v-gl-tooltip
-      class="btn btn-default append-right-10 js-edit-button ml-2"
+      category="primary"
+      variant="default"
+      class="append-right-10 js-edit-button ml-2 pb-2"
       :title="__('Edit this release')"
       :href="editLink"
     >
       <icon name="pencil" />
-    </gl-link>
+    </gl-button>
   </div>
 </template>

changelogs/unreleased/216477-gllink-updates.yml

+---
+title: Update style of buttons on the Releases page
+merge_request: 31129
+author: Özgür Adem Işıklı @iozguradem
+type: changed