feat: implement InternalAppService for Knative app lifecycle

[AdilFayyaz]

Depends on: #7166

Why are the changes needed?

Apps need a data plane implementation that manages long-running containerized workloads (serving endpoints, LLM inference, dashboards) via Knative KService CRDs, with no database dependency — all app state lives in K8s.

What changes were proposed in this pull request?

• Update app/config/config.go to expose the Base Domain for Ingress
• Update app/internal/k8s/app_client.go: extend List with K8s continue-token pagination (limit/token params, client.Limit/client.Continue options) and extend Watch with optional appName label filter for single-app scoping
• Add app/internal/service/internal_app_service.go implementing all AppService
  RPCs against the K8s client: Create (deploy + return PENDING + deterministic public URL), Get, Update (branches on Spec.DesiredState — STOPPED calls Stop, otherwise Deploy), Delete, List (project/domain filter + pagination), Watch\ (initial snapshot + live K8s event stream)
• Add app/internal/setup.go wiring the above behind a feature flag and mounting the handler at /internal/flyteidl2.app.AppService/ to avoid collision with the control-plane AppService on the same mux

How was this patch tested?

• go test ./app/internal/k8s/... — existing 19 tests verify List pagination and Watch appName filter changes don't regress
• go test ./app/internal/service/... — 16 new tests covering all InternalAppService RPCs: validation, DesiredState branching in Update, pagination in List, initial snapshot + AppId scoping in Watch (uses httptest + real connect client for streaming)

Setup process

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

Docs link

• main
  • Flyte 2 WIP #6583
    • feat: add AppK8sClient for KService lifecycle management #7166
      • feat: implement InternalAppService for Knative app lifecycle 👈
        • feat: implement AppService control plane proxy with TTL cache #7176
          • feat: resilient Watch RPC with reconnect and resourceVersion tracking #7188
            • feat: path based ingress routing for Flyte apps via Traefik + Knative #7197