feat: add Azure Front Door backend attachment APIs

[Ramkumar Chinchani (rchincha)]

What type of PR is this?

What this PR does / why we need it:

Towards GEP-4894

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

Special notes for your reviewer

[codecov]

Codecov Report

❌ Patch coverage is 47.77328% with 129 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.68%. Comparing base (c897e4c) to head (60c7747).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
.../hub/azurefrontdoorbackendattachment/controller.go	50.64%	101 Missing and 14 partials ⚠️
cmd/hub-net-controller-manager/main.go	0.00%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #406      +/-   ##
==========================================
- Coverage   66.82%   65.68%   -1.15%     
==========================================
  Files          33       35       +2     
  Lines        3783     4106     +323     
==========================================
+ Hits         2528     2697     +169     
- Misses       1078     1213     +135     
- Partials      177      196      +19     

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