test: add more traffic manager e2e tests

[zhiying-lin]

What type of PR is this?
/kind test

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Requirements:

• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• includes documentation
• adds unit tests

How has this code been tested

https://github.com/Azure/fleet-networking/actions/runs/12481424602

Special notes for your reviewer

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.78%. Comparing base (153b55b) to head (f18e1e0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #239      +/-   ##
==========================================
- Coverage   80.07%   79.78%   -0.29%     
==========================================
  Files          27       27              
  Lines        3844     3844              
==========================================
- Hits         3078     3067      -11     
- Misses        611      621      +10     
- Partials      155      156       +1     

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[Copilot]

Copilot reviewed 5 out of 8 changed files in this pull request and generated 1 comment.

Files not reviewed (3)

• pkg/controllers/hub/trafficmanagerbackend/controller_integration_test.go: Evaluated as low risk
• pkg/controllers/hub/trafficmanagerprofile/controller_integration_test.go: Evaluated as low risk
• test/common/trafficmanager/azureprovider/profile.go: Evaluated as low risk

Comments suppressed due to low confidence (1)

test/e2e/framework/workload_manager.go:206

• The 'AddServiceDNSLabel' function should have a test case to ensure it works as expected.

func (wm *WorkloadManager) AddServiceDNSLabel(ctx context.Context, cluster *Cluster) error {