Follow-up Tasks for MachinePool support in ClusterClass

[willie-yao]

What would you like to be added (User Story)?

This is a follow up to #5991 to track the remaining follow-up tasks for adding MachinePool support in ClusterClass.

Detailed Description

### Unit Tests
- [x] internal/controllers/topology/cluster/scope/state_test.go #10052 @willie-yao
- [x] internal/controllers/topology/cluster/scope/upgradetracker_test.go #10052 @willie-yao
- [x] internal/topology/check/compatibility_test.go #10052 @willie-yao
- [x] internal/webhooks/cluster_test.go #10055 @willie-yao
- [x] internal/webhooks/clusterclass_test.go #10055 @willie-yao
- [x] internal/webhooks/patch_validation_test.go #10055 @willie-yao
- [x] internal/controllers/clusterclass/clusterclass_controller_test.go #10055 @willie-yao
- [ ] test/extension/handlers/topologymutation/handler_test.go #10216 @willie-yao
- [ ] cmd/clusterctl/client/cluster/topology_test.go #10216 @willie-yao
- [ ] Run unit & integration tests with coverage and check if we missed something

### E2E Tests
- [x] ClusterClass changes & rollout (clusterclass_changes.go & clusterclass_rollout, flavor: "topology") #9703
- [x] clusterctl upgrade (clusterctl_upgrade.go, workload flavor: "topology") #9892
- [x] Runtime SDK (cluster_upgrade_runtimesdk.go, flavor: "upgrades-runtimesdk") #9703
- [x] Self-hosted (self_hosted.go, flavor: "topology") #9540
- [ ] Autoscaler (autoscaler.go, flavor: "topology-autoscaler") #10083
- [ ] Dualstack e2e tests #10135
- [ ] Audit if there are any Cluster YAMLs left in the test folder which don't have a machinePool in Cluster.spec.topology

### Misc/Documentation
- [ ] TBD: internal/controllers/topology/machinepool might be not needed as MachinePool.reconcileDelete deletes templates
- [ ] Update proposal
- [ ] Update docs (probably mostly book)

Later

• TBD: consider de-duplicating MD/MP code
• TBD: MachinePool upgrading use Node list instead of Node get
• MHC for MachinePools: depends on MachinePool Machines

Anything else you would like to add?

No response

Label(s) to be applied

/kind feature