Fix restoration of infra with migrated network layout

[plkokanov]

How to categorize this PR?

/area control-plane-migration
/kind bug
/platform azure

What this PR does / why we need it:
This PR modifies the layout mutator which adds the migration.azure.provider.extensions.gardener.cloud/zone annotation on the Infrastructure resource so that the annotation is also added during the restore phase of control plane migration in the following cases:

1. If the .status.state field is defined and is in the azure.provider.extensions.gardener.cloud/v1alpha1 group version, then
   • If its .data field contains an entry for migration.azure.provider.extensions.gardener.cloud/zone, then this entry is added as an annotation to the Infrastructure resource
2. If the .status.state field is defined and its type is InfrastructureState, then
   • If this .state field contains a .savedProviderStatus field and its .networks.subnets array contains a subnet for which the .migrated field is true and the .zone field is not nil

Additionally, during reconciliation, if the new flow reconciler is used and the migration.azure.provider.extensions.gardener.cloud/zone annotation is present on the Infrastructure resource, then it is persisted in the .status.state.data map.

Which issue(s) this PR fixes:
Fixes #827

Special notes for your reviewer:

Release note:

Fixed an issue that prevented the `Infrastructure` resource to be correctly restored during control plane migration, if the `Infrastructure` was previously migrated from a single subnet network layout to a multiple subnet network layout.

[gardener-robot]

@plkokanov You need rebase this pull request with latest master branch. Please check.

[plkokanov]

/hold
I want to do a few more tests of the changes.

[plkokanov]

I finally have time to come back to this and I have done the following tests all of which passed without issues:

---

1. Create a cluster with 1 zone and 1 subnet layout using the terraform reconciler.
2. Migrate the cluster from single zone layout to multiple zone layout, which adds the migration.azure.provider.extensions.gardener.cloud/zone annotation.
3. Perform control plane migration to a destination seed which also uses the terraform reconciler.
4. Check that the infrastructure resource is created on the destination seed with the correct (preserved) migration.azure.provider.extensions.gardener.cloud/zone annotation.

---

1. Create a cluster with 1 zone and 1 subnet layout using the flow reconciler (seed has azure.provider.extensions.gardener.cloud/use-flow: "new" annotation)
2. Migrate the cluster from single zone layout to multiple zone layout.
3. Perform control plane migration to a destination seed which also uses the flow reconciler (seed has azure.provider.extensions.gardener.cloud/use-flow: "new" annotation)
4. Check that the infrastructure resource is created on the destination seed with the correct (preserved) migration.azure.provider.extensions.gardener.cloud/zone annotation.

---

1. Create a cluster with 1 zone and 1 subnet layout using the terraform reconciler.
2. Migrate the cluster from single zone layout to multiple zone layout.
3. Perform control plane migration to a destination seed which uses the flow reconciler for new shoots (seed has azure.provider.extensions.gardener.cloud/use-flow: "new" annotation)
4. Check that the infrastructure resource is created on the destination seed with the correct (preserved) migration.azure.provider.extensions.gardener.cloud/zone annotation.

---

@kon-angelo, does it make sense to preform similar tests when migrating the control plane from a seed that uses the flow reconciler to a seed that uses the terraform reconciler (if that is even supported)?

In the tests above, would it make a difference if the annotation used to enable the flow reconciler is azure.provider.extensions.gardener.cloud/use-flow: "true" vs azure.provider.extensions.gardener.cloud/use-flow: "new"

[plkokanov]

/unhold