Use Service port in generated Kong services

[rainest]

What this PR does / why we need it:

Uses the Service port from the Ingress(like) backend for the Kong service port. Previously we used 80 as a universal default.

This is a cosmetic change. As all KIC-generated services use upstreams, the service port is ignored in favor of the upstream's targets' ports, which are set to the Service's Endpoints' ports.

Which issue this PR fixes:

Fix #4470

Special notes for your reviewer:

This change still uses the 80 default when initially generating services, e.g. in the Ingress translator. Because Ingress(like) backends may use port names instead of numbers, we don't necessarily know the port number until we look up the Service.

We look up Services when generating upstreams, so this moves upstream generation before service generation. I don't love updating the map values in place and returning a new copy, but we were already passing the map by value and don't use the Kong service during upstream generation (we use the attached ServicePort instead).

Moving upstream generation before the skipped services list also feels a bit weird, but apparently we were never using the skipped service list during upstream generation anyway? We were apparently generating some upstreams we weren't actually using, but this probably doesn't matter--worst case I guess you get a bunch of config bloat if you make tons of misconfigured Services, and the fix is "don't do that, it's silly".

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Patch coverage: 100.0% and no project coverage change.

Comparison is base (758be7c) 67.6% compared to head (ba5a2e5) 67.7%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #4503   +/-   ##
=====================================
  Coverage   67.6%   67.7%           
=====================================
  Files        161     161           
  Lines      18839   18846    +7     
=====================================
+ Hits       12751   12763   +12     
+ Misses      5327    5324    -3     
+ Partials     761     759    -2     

Files Changed	Coverage Δ
internal/dataplane/parser/parser.go	83.0% <100.0%> (-0.6%)	⬇️

... and 3 files with indirect coverage changes

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