feat: add --gateway-discovery-dns-strategy flag

[pmalek]

What this PR does / why we need it:

This PR introduces --gateway-discovery-dns-strategy flag which allow users to specify which strategy to use when creating address of Admin API endpoints.

There are 3 options that are accepted as values for this flag:

• service - for service scoped pod dns names: pod-ip-address.service-name.my-namespace.svc.cluster-domain.example
• pod - for namespace scope pod dns names: pod-ip-address.my-namespace.pod.cluster-domain.example
• ip (default, retains v2.9 behavior) - for regular IP addresses

Which issue this PR fixes:

closes: #4065

Special notes for your reviewer:

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: 78.3% and project coverage change: +60.1 🎉

Comparison is base (74b39d2) 0.0% compared to head (6d58c30) 60.1%.

Additional details and impacted files

@@           Coverage Diff           @@
##           main   #4071      +/-   ##
=======================================
+ Coverage      0   60.1%   +60.1%     
=======================================
  Files         0     151     +151     
  Lines         0   16608   +16608     
=======================================
+ Hits          0    9990    +9990     
- Misses        0    5987    +5987     
- Partials      0     631     +631     

Impacted Files	Coverage Δ
internal/manager/config_validation.go	83.5% <0.0%> (ø)
internal/manager/setup.go	40.5% <0.0%> (ø)
...ntrollers/configuration/kongadminapi_controller.go	62.3% <23.0%> (ø)
internal/manager/config/types/dnsstrategy.go	83.3% <83.3%> (ø)
internal/adminapi/endpoints.go	88.1% <91.6%> (ø)
internal/manager/config.go	94.6% <100.0%> (ø)
internal/manager/controllerdef.go	98.8% <100.0%> (ø)
internal/util/builder/endpointport.go	100.0% <100.0%> (ø)

... and 143 files with indirect coverage changes

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