chore(*) make port validation consistent

[jpeach]

Summary

Introduce a helper to make TCP/UDP port validation checks
consistent across the API.

Full changelog

N/A

Issues resolved

N/A

Documentation

N/A

Testing

• Unit tests
• E2E tests
• Manual testing on Universal
• Manual testing on Kubernetes

Backwards compatibility

• Add backport-to-stable label if the code is backwards compatible. Otherwise, list breaking changes.

[codecov-commenter]

Codecov Report

Merging #2448 (bda1cad) into master (9e8e2b7) will increase coverage by 0.09%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##           master    #2448      +/-   ##
==========================================
+ Coverage   52.52%   52.62%   +0.09%     
==========================================
  Files         879      879              
  Lines       47923    47918       -5     
==========================================
+ Hits        25170    25215      +45     
+ Misses      20710    20651      -59     
- Partials     2043     2052       +9     

Impacted Files	Coverage Δ
pkg/core/resources/apis/mesh/mesh_validator.go	85.00% <0.00%> (+0.60%)	⬆️
...kg/core/resources/apis/mesh/dataplane_validator.go	93.78% <100.00%> (+0.92%)	⬆️
...e/resources/apis/mesh/externalservice_validator.go	100.00% <100.00%> (ø)
pkg/core/resources/apis/mesh/validators.go	90.82% <100.00%> (+0.44%)	⬆️
...core/resources/apis/mesh/zone_ingress_validator.go	85.18% <100.00%> (+5.18%)	⬆️
pkg/mads/v1/client/client.go	41.25% <0.00%> (-2.50%)	⬇️
api/observability/v1/mads.pb.go	34.53% <0.00%> (-1.04%)	⬇️
pkg/xds/generator/direct_access_proxy_generator.go	83.90% <0.00%> (+1.14%)	⬆️
pkg/core/resources/model/rest/resource.go	69.23% <0.00%> (+1.28%)	⬆️
api/mesh/v1alpha1/dataplane.pb.go	37.85% <0.00%> (+2.01%)	⬆️
... and 8 more

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[lobkovilya]

Looks good! Please add the same for externalservice_validator.go