Handling of unbound ServerClaims

[defo89]

Describe the bug
We can patch the MetalMachine .spec.ProviderId after ServerClaim is bound to a Server. If claim is Unbound, we might want to wait or requeue until it's bound.

2024-07-31T13:04:30Z	INFO	Created or Patched ServerClaim	{"ServerClaim": "metalmachinetemplate-sample-control-plane-s4c9p", "Operation": "unchanged"}
2024-07-31T13:04:30Z	INFO	Patching ProviderID in MetalMachine
2024-07-31T13:04:30Z	INFO	Observed a panic in reconciler: runtime error: invalid memory address or nil pointer dereference	{"controller": "metalmachine", "controllerGroup": "infrastructure.cluster.x-k8s.io", "controllerKind": "MetalMachine", "MetalMachine": {"name":"metalmachinetemplate-sample-control-plane-s4c9p","namespace":"default"}, "namespace": "default", "name": "metalmachinetemplate-sample-control-plane-s4c9p", "reconcileID": "fc8037e4-78ae-47ff-8c38-498abdc48bb5"}
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x1a0c98a]

goroutine 91 [running]:
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile.func1()
	/Users/user/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:111 +0x1e5
panic({0x1be5a00?, 0x326a360?})
	/Users/user/sdk/go1.22.5/src/runtime/panic.go:770 +0x132
github.com/ironcore-dev/cluster-api-provider-metal/internal/controller.(*MetalMachineReconciler).patchMetalMachineProviderID(0xc0000110f8, {0x21c9d40, 0xc00017c600}, 0xc0009290c8, 0xc0005b43c0, 0xc000931b80)
	/Users/user/go/src/github.com/ironcore-dev/cluster-api-provider-metal/internal/controller/metalmachine_controller.go:333 +0x6a
github.com/ironcore-dev/cluster-api-provider-metal/internal/controller.(*MetalMachineReconciler).reconcileNormal(0xc0000110f8, {0x21c9d40, 0xc00017c600}, 0xc0005f5220, 0xc000564288?)
	/Users/user/go/src/github.com/ironcore-dev/cluster-api-provider-metal/internal/controller/metalmachine_controller.go:237 +0x436
github.com/ironcore-dev/cluster-api-provider-metal/internal/controller.(*MetalMachineReconciler).Reconcile(0xc0000110f8, {0x21c9d40, 0xc00017c600}, {{{0xc000910d26?, 0x5?}, {0xc0009342a0?, 0xc00090dd10?}}})
	/Users/user/go/src/github.com/ironcore-dev/cluster-api-provider-metal/internal/controller/metalmachine_controller.go:157 +0xc25
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile(0x21cfed8?, {0x21c9d40?, 0xc00017c600?}, {{{0xc000910d26?, 0xb?}, {0xc0009342a0?, 0x0?}}})
	/Users/user/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:114 +0xb7
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler(0xc0001ddd90, {0x21c9d78, 0xc00001c780}, {0x1c937c0, 0xc00031e060})
	/Users/user/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:311 +0x3bc
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem(0xc0001ddd90, {0x21c9d78, 0xc00001c780})
	/Users/user/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:261 +0x1be
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2()
	/Users/user/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:222 +0x79
created by sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2 in goroutine 113
	/Users/user/go/pkg/mod/sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:218 +0x486