feat: add events to the trafficManagerBackend controller

[Copilot]

This PR adds event recording to the trafficManagerBackend controller, following the same pattern used in the trafficmanagerprofile controller. Events are now emitted for important state changes and operations:

Added events for:

• Successfully configuring endpoints in Azure Traffic Manager
• Removing all endpoints due to zero weight setting
• Deletion of Azure Traffic Manager endpoints
• Various error conditions (profile not found, service import not found, API failures)

Implementation details:

• Added constants for event reasons (backendEventReasonAccepted, backendEventReasonDeleted, backendEventReasonAzureAPIError)
• Added ControllerName constant for use in event recording
• Added EventRecorder field to the Reconciler struct
• Initialized EventRecorder in main.go
• Added event recording in key functions:
  • handleDelete
  • handleUpdate
  • validateTrafficManagerProfile
  • validateAzureTrafficManagerProfile
  • validateServiceImportAndCleanupEndpointsIfInvalid
• Added validation helpers for testing events in integration tests

These events will help users and operators understand the status and lifecycle of the trafficManagerBackend resources and troubleshoot issues when they occur.

Fixes #306.

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

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• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
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---

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[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 80.48%. Comparing base (af25d4f) to head (50a233b).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ontrollers/hub/trafficmanagerbackend/controller.go	72.72%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #312      +/-   ##
==========================================
+ Coverage   80.30%   80.48%   +0.17%     
==========================================
  Files          29       29              
  Lines        4108     4161      +53     
==========================================
+ Hits         3299     3349      +50     
- Misses        643      647       +4     
+ Partials      166      165       -1     

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