Test(e2e): List entities instead of dump.Get to fetch Kong config in e2e tests

[randmonkey]

What this PR does / why we need it:

List Services, Routes, Upstreams and Targets to verify Kong configuration in gateway pods in verifyIngressWithEchoBackendsInAdminAPI instead of dump.Get. This could reduce the concurrency of streams to forwarded ports.

e2e run passes: https://github.com/Kong/kubernetes-ingress-controller/actions/runs/10173800539.

Which issue this PR fixes:

Fixes #6317
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 No need to update changelog.

[team-k8s-bot]

E2E (targeted) tests with KIND-based clusters were started at https://github.com/Kong/kubernetes-ingress-controller/actions/runs/10160735452

[team-k8s-bot]

E2E (targeted) tests with KIND-based clusters were started at https://github.com/Kong/kubernetes-ingress-controller/actions/runs/10173800539

[team-k8s-bot]

E2E (targeted) tests with KIND-based clusters were started at https://github.com/Kong/kubernetes-ingress-controller/actions/runs/10191095350

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

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[team-k8s-bot]

E2E (targeted) tests with KIND-based clusters were started at https://github.com/Kong/kubernetes-ingress-controller/actions/runs/10193698357