Resolve "Follow up - Add Vuex to customizable cycle analytics"

What does this MR do?

We introduced the Custom stages for cycle analytics form UI in !15216 (merged) this requires a request for groupLabels. We also refactored the ui for cycle analytics from HAML+vue to just haml in !15039 (merged) which also introduced Vuex to analytics/cycle_analytics for state management.

This MR:

• Refactors the group label request to use Vuex
• Replaces the gon.features check with the glFeatureFlags mixin
• Differentiates between stage events and custom form events (coming in !17496 (closed))
• Fixes timeouts with the limit warning spec
• Adds a spec that was missed for changing the currently selected cycle analytics stage
• Removes the custom_stage_form_container which was a temporary solution before we finished the refactor

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #32019 (closed)

ee/app/assets/javascripts/analytics/cycle_analytics/components/stage_card_list_item.vue

@@ -21,10 +21,10 @@ export default {
   },
   computed: {
     activeClass() {
-      return 'active font-weight-bold border-style-solid border-color-blue-300';
+      return 'active font-weight-bold border-color-blue-300';
     },
     inactiveClass() {
-      return 'bg-transparent border-style-dashed border-color-default';
+      return 'bg-transparent border-color-default';
     },
   },
 };
@@ -33,7 +33,7 @@ export default {
 <template>
   <div
     :class="[isActive ? activeClass : inactiveClass]"
-    class="stage-nav-item d-flex pl-4 pr-4 m-0 mb-1 ml-2 rounded border-width-1px"
+    class="stage-nav-item d-flex pl-4 pr-4 m-0 mb-1 ml-2 rounded border-width-1px border-style-solid"
   >
     <slot></slot>
     <div v-if="canEdit" class="dropdown">