interface: add a weight field to internalServiceExport

[zhiying-lin]

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

What this PR does / why we need it:
Add a new field to support serviceExport weight feature

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 79.80%. Comparing base (59f1704) to head (50b1d82).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #249   +/-   ##
=======================================
  Coverage   79.80%   79.80%           
=======================================
  Files          28       28           
  Lines        3863     3863           
=======================================
  Hits         3083     3083           
  Misses        623      623           
  Partials      157      157           

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