interface: use the annotation to support serviceExport weight

[zhiying-lin]

What type of PR is this?
/kind api-change

What this PR does / why we need it:
As discussed, since the exportedLabel and exportedAnnotation are used for the derived service.
We'll put the weight on the serviceExport annotation instead.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 80.14%. Comparing base (f98e10e) to head (54d62ea).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #247      +/-   ##
==========================================
+ Coverage   79.88%   80.14%   +0.25%     
==========================================
  Files          28       28              
  Lines        3863     3863              
==========================================
+ Hits         3086     3096      +10     
+ Misses        620      611       -9     
+ Partials      157      156       -1     

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