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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internal/version/version.go

@@ -6,9 +6,10 @@ import (
 	"runtime/debug"
 )
 
-func ClientImage() string {
-	return "ghcr.io/netbirdio/netbird:0.71.4@sha256:c4195811bf9999544db5176950a0d6513c880d0195450b59eb156c254e0dd3b5"
-}
+const (
+	NetbirdClientImage = "ghcr.io/netbirdio/netbird:0.71.4@sha256:c4195811bf9999544db5176950a0d6513c880d0195450b59eb156c254e0dd3b5"
+	KubeApiProxyImage  = "ghcr.io/netbirdio/netbird-kubeapi-proxy:v0.0.1@sha256:aa5bbdfc2eca51438f3d50ed4441d61388e9a8d2d5dc886cc4988dacd36ad648"
+)
 
 func BuildVersion() string {
 	bi, ok := debug.ReadBuildInfo()

internal/version/version_test.go

@@ -13,7 +13,7 @@ import (
 	"github.com/go-openapi/testify/v2/require"
 )
 
-func TestClientImage(t *testing.T) {
+func TestNetbirdClientImage(t *testing.T) {
 	t.Parallel()
 
 	b, err := os.ReadFile("../../go.mod")
@@ -26,10 +26,9 @@ func TestClientImage(t *testing.T) {
 	require.GreaterT(t, idx, -1)
 	modVersion := strings.TrimPrefix(f.Require[idx].Mod.Version, "v")
 
-	clientImg := ClientImage()
-	start := strings.Index(clientImg, ":") + 1
-	end := strings.Index(clientImg, "@")
-	imgVersion := clientImg[start:end]
+	start := strings.Index(NetbirdClientImage, ":") + 1
+	end := strings.Index(NetbirdClientImage, "@")
+	imgVersion := NetbirdClientImage[start:end]
 
 	require.EqualT(t, modVersion, imgVersion)
 }