feat: add metrics (2/)

[michaelawyu]

What type of PR is this?

/kind test
/kind feature

What this PR does / why we need it:

This PR is the second part of a series of PRs that add metrics to Fleet networking controllers. As a part of the change, this PR also:

• refactors integration tests for several controllers, most importantly ServiceExport, EndpointSlice, InternalServiceExport, and EndpointSliceImport
• fixes a number of issues that leads to flaky integration tests

Which issue(s) this PR fixes:

N/A

Requirements:

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

How has this code been tested

[x] Unit tests
[x] Integration tests

Special notes for your reviewer

See #128 for the previous PR.

[codecov]

Codecov Report

Merging #136 (d931d3c) into main (54fe6e1) will increase coverage by 1.11%.
The diff coverage is 89.23%.

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
+ Coverage   78.08%   79.20%   +1.11%     
==========================================
  Files          20       20              
  Lines        2551     2712     +161     
==========================================
+ Hits         1992     2148     +156     
- Misses        440      448       +8     
+ Partials      119      116       -3     

Impacted Files	Coverage Δ
...rollers/member/internalserviceexport/controller.go	83.84% <84.74%> (+8.84%)	⬆️
...ntrollers/member/endpointsliceimport/controller.go	79.92% <92.95%> (+6.44%)	⬆️
...ntrollers/member/endpointsliceexport/controller.go	80.64% <0.00%> (-2.41%)	⬇️
...rollers/member/internalserviceimport/controller.go	75.43% <0.00%> (-2.34%)	⬇️
pkg/controllers/member/serviceimport/controller.go	68.11% <0.00%> (-1.59%)	⬇️
pkg/controllers/hub/serviceimport/controller.go	72.85% <0.00%> (-0.87%)	⬇️
...ontrollers/hub/internalserviceexport/controller.go	77.97% <0.00%> (-0.82%)	⬇️
...rollers/member/internalmembercluster/controller.go	70.77% <0.00%> (-0.75%)	⬇️
.../controllers/hub/endpointsliceexport/controller.go	69.77% <0.00%> (-0.42%)	⬇️
...ontrollers/hub/internalserviceimport/controller.go	77.38% <0.00%> (+1.07%)	⬆️
... and 4 more

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