Add namespace to external etcd ref

[rahulbabu95]

Description of changes:
In the etcdadm reconcile loop we make a namespaced lookup for the etcdadm cluster object referenced in the capi cluster. For Cloudstack provider, when we create the capi cluster object we missed referencing the namespace as we do for other providers. This fix adds in the namespace for the external etcd reference.

This was the panic on the etcd controller before the fix:

2025-02-17T19:07:35Z    ERROR   controllers.EtcdadmCluster      Failed to get etcdadm cluster   {"etcdadmcluster": {"name":"rahul-mgmt-cs-etcd"}, "error": "an empty namespace may not be set when a resource name is provided"}
github.com/aws/etcdadm-controller/controllers.(*EtcdadmClusterReconciler).Reconcile
        github.com/aws/etcdadm-controller/controllers/controller.go:127
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Reconcile
        sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:119
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler
        sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:316
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem
        sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:266
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2
        sigs.k8s.io/[email protected]/pkg/internal/controller/controller.go:227

Testing (if applicable):
Built a new etcd controller and verified that the panic went away during the reconciliation.

Documentation added/planned (if applicable):

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.35%. Comparing base (b90922c) to head (fa49138).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9252   +/-   ##
=======================================
  Coverage   72.35%   72.35%           
=======================================
  Files         587      587           
  Lines       46140    46140           
=======================================
  Hits        33385    33385           
  Misses      11006    11006           
  Partials     1749     1749           

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[2ez4szliu]

/lgtm
/approve

[eks-distro-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 2ez4szliu

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[rahulbabu95]

/cherrypick release-0.21

[eks-distro-pr-bot]

@rahulbabu95: new pull request created: #9261

In response to this:

/cherrypick release-0.21

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