Add new resource for Kubernetes API proxy (#279)

This adds a new resource which deploys a Kubernetes API server proxy
that can be used to access the API server without tokens through
Netbird.

Part of #274 

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## Summary by CodeRabbit

* **New Features**
* Added ClusterProxy custom resource for cluster API proxying
capabilities

* **Documentation**
  * Added ClusterProxy API reference documentation with schema details

* **Examples**
* Added example ClusterProxy configuration and RBAC setup for cluster
proxy targets

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pkg/applyconfigurations/api/v1alpha1/clusterproxyspec.go

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by controller-gen. DO NOT EDIT.
+
+package v1alpha1
+
+// ClusterProxySpecApplyConfiguration represents a declarative configuration of the ClusterProxySpec type for use
+// with apply.
+//
+// ClusterProxySpec defines the desired state of ClusterProxy.
+type ClusterProxySpecApplyConfiguration struct {
+	// ClusterName is the name of the Kubernetes cluster.
+	ClusterName *string `json:"clusterName,omitempty"`
+	// APIServer is the URL of the Kubernetes API server to proxy requests to.
+	APIServer *string `json:"apiServer,omitempty"`
+	// ServiceAccountName is a reference to the service account used for impersonation.
+	ServiceAccountName *string `json:"serviceAccountName,omitempty"`
+}
+
+// ClusterProxySpecApplyConfiguration constructs a declarative configuration of the ClusterProxySpec type for use with
+// apply.
+func ClusterProxySpec() *ClusterProxySpecApplyConfiguration {
+	return &ClusterProxySpecApplyConfiguration{}
+}
+
+// WithClusterName sets the ClusterName field in the declarative configuration to the given value
+// and returns the receiver, so that objects can be built by chaining "With" function invocations.
+// If called multiple times, the ClusterName field is set to the value of the last call.
+func (b *ClusterProxySpecApplyConfiguration) WithClusterName(value string) *ClusterProxySpecApplyConfiguration {
+	b.ClusterName = &value
+	return b
+}
+
+// WithAPIServer sets the APIServer field in the declarative configuration to the given value
+// and returns the receiver, so that objects can be built by chaining "With" function invocations.
+// If called multiple times, the APIServer field is set to the value of the last call.
+func (b *ClusterProxySpecApplyConfiguration) WithAPIServer(value string) *ClusterProxySpecApplyConfiguration {
+	b.APIServer = &value
+	return b
+}
+
+// WithServiceAccountName sets the ServiceAccountName field in the declarative configuration to the given value
+// and returns the receiver, so that objects can be built by chaining "With" function invocations.
+// If called multiple times, the ServiceAccountName field is set to the value of the last call.
+func (b *ClusterProxySpecApplyConfiguration) WithServiceAccountName(value string) *ClusterProxySpecApplyConfiguration {
+	b.ServiceAccountName = &value
+	return b
+}