feat: add telemetry to answer for user failed to find template (#6489)

## Summary

Adds mixpanel telemetry with goal of: "We currently only know when a
user opens a template workflow. But we also want to know if they failed
to find what they want"

Example mixpanel query: 

```
app:template_library_closed
  WHERE template_selected = false AND time_spent_seconds >= 10
  ```

But can drill down further into what filters were selected etc to answer what they were looking for but couldn't find. 

```
 1. Event: app:template_filter_changed
  2. Filter:
- Add formula: "Where user also triggered app:template_library_closed
with template_selected = false in same session"
  3. Breakdown by: search_query
  4. Sort by: Total Count (descending)

  Search Query           Failed Sessions
  -----------------------------------
  "flux video"             45 times
  "sdxl controlnet"     32 times
  "upscaler"               28 times
  (empty/just filter)   20 times
```

```
 Event: app:template_filter_changed
  WHERE filtered_count = 0
    AND user did app:template_library_closed
    with template_selected = false

  Breakdown by: search_query
  ```
  etc.


https://www.notion.so/comfy-org/Number-of-users-who-open-the-template-library-and-where-do-they-click-29b6d73d36508044a595c0fb653ca6dc?source=copy_link

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6489-feat-add-telemetry-to-answer-for-user-failed-to-find-template-29d6d73d365081cdad72fd7c6ada5dc7)
by [Unito](https://www.unito.io)

src/platform/telemetry/providers/cloud/MixpanelTelemetryProvider.ts

@@ -26,6 +26,7 @@ import type {
   TelemetryProvider,
   TemplateFilterMetadata,
   TemplateLibraryMetadata,
+  TemplateLibraryClosedMetadata,
   TemplateMetadata,
   WorkflowImportMetadata
 } from '../../types'
@@ -235,6 +236,10 @@ export class MixpanelTelemetryProvider implements TelemetryProvider {
     this.trackEvent(TelemetryEvents.TEMPLATE_LIBRARY_OPENED, metadata)
   }
 
+  trackTemplateLibraryClosed(metadata: TemplateLibraryClosedMetadata): void {
+    this.trackEvent(TelemetryEvents.TEMPLATE_LIBRARY_CLOSED, metadata)
+  }
+
   trackWorkflowImported(metadata: WorkflowImportMetadata): void {
     this.trackEvent(TelemetryEvents.WORKFLOW_IMPORTED, metadata)
   }