[Discover] Restore the default Discover alert action for Observabilit…

…y profile (#204755)

- Closes #203113

## Summary

Previously in Observability profile "Create custom threshold rule"
action replaced the "Create search threshold rule" action. With this PR,
both actions will be available.

<img width="611" alt="Screenshot 2024-12-18 at 14 12 39"
src="https://github.com/user-attachments/assets/ad24194a-92cb-41a3-b6b3-f9d8bf6be314"
/>

---------

Co-authored-by: Davis McPhee <[email protected]>

src/platform/plugins/shared/discover/public/context_awareness/profile_providers/observability/observability_root_profile/accessors/get_app_menu.ts

@@ -78,14 +78,14 @@ const registerCustomThresholdRuleAction = (
   { dataView }: AppMenuExtensionParams
 ) => {
   registry.registerCustomActionUnderSubmenu(AppMenuActionId.alerts, {
-    id: AppMenuActionId.createRule,
+    id: 'custom-threshold-rule',
     type: AppMenuActionType.custom,
     order: 101,
     controlProps: {
       label: i18n.translate('discover.observabilitySolution.appMenu.customThresholdRule', {
         defaultMessage: 'Create custom threshold rule',
       }),
-      iconType: 'visGauge',
+      iconType: 'bell',
       testId: 'discoverAppMenuCustomThresholdRule',
       onClick: ({ onFinishAction }) => {
         const index = dataView?.toMinimalSpec();
@@ -127,7 +127,7 @@ const registerCreateSLOAction = (
         label: i18n.translate('discover.observabilitySolution.appMenu.slo', {
           defaultMessage: 'Create SLO',
         }),
-        iconType: 'bell',
+        iconType: 'visGauge',
         testId: 'discoverAppMenuCreateSlo',
         onClick: ({ onFinishAction }) => {
           const index = dataView?.getIndexPattern();