chore: add enable v1alpha1 flag back for backward compatibility with CCP

[weng271190436]

What type of PR is this?

Add back enable v1alpha1 flag removed from last PR to be backward compatible with CCP chart in AKS RP
#343

/kind cleanup

/kind deprecation
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

Special notes for your reviewer

[codecov]

Codecov Report

❌ Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 66.74%. Comparing base (f1a1f82) to head (cdfff0e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/mcs-controller-manager/main.go	0.00%	3 Missing ⚠️
cmd/member-net-controller-manager/main.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #344      +/-   ##
==========================================
- Coverage   67.64%   66.74%   -0.91%     
==========================================
  Files          33       33              
  Lines        4884     3786    -1098     
==========================================
- Hits         3304     2527     -777     
+ Misses       1403     1082     -321     
  Partials      177      177              

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