Add telemetry to Chat Customizations editor (#301173)

* Add telemetry to Chat Customizations editor

Instrument 7 key user interactions in the AI Customization Management
Editor with GDPR-compliant publicLog2 telemetry events:

- chatCustomizationEditor.opened: tracks editor opens with initial section
- chatCustomizationEditor.sectionChanged: tracks sidebar navigation
- chatCustomizationEditor.itemSelected: tracks item selection with type/storage
- chatCustomizationEditor.createItem: tracks AI-guided and manual creation
- chatCustomizationEditor.saveItem: tracks save actions (builtin override + existing)
- chatCustomizationEditor.deleteItem: tracks confirmed deletions
- chatCustomizationEditor.search: tracks search usage with result counts

Co-authored-by: Copilot <[email protected]>

* fix: improve search telemetry logging in Chat Customizations editor

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Co-authored-by: Copilot <[email protected]>