Add NetBird server to test connections (#328)

This change adds a NetBird server to the e2e test and ensures that
cluster proxy peers can start and connect to the server.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Changes**
* Updated the `ClusterProxy` `spec.apiServer` default to include a
trailing `/` when omitted, aligning operator behavior with the
Kubernetes in-cluster API URL.
* **Documentation**
* Refreshed the `ClusterProxySpec.apiServer` API reference to reflect
the trailing `/` default.
* **Tests**
* Improved end-to-end coverage with a dynamically provisioned management
URL, more robust readiness polling, and enhanced `ClusterProxy`
validation.
* **Chores**
* Updated the end-to-end test Go configuration and CI to use the
e2e-specific Go settings/toolchain.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

pkg/version/version.go

@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: BSD-3-Clause
+
+package version
+
+import (
+	"runtime/debug"
+)
+
+const (
+	NetbirdClientImage = "ghcr.io/netbirdio/netbird:0.72.4@sha256:6c6c20baffae4a3ec50f29ec9361608a420625185505e8cd6f0c44d71c5d4798"
+	KubeApiProxyImage  = "ghcr.io/netbirdio/netbird-kubeapi-proxy:v0.0.4@sha256:bffa4f093abc19b4934ae37657bac76fa3b390cbd39aadac987634215eb750f5"
+)
+
+func BuildVersion() string {
+	bi, ok := debug.ReadBuildInfo()
+	if !ok {
+		return "unknown"
+	}
+
+	modified := true
+	for _, s := range bi.Settings {
+		if s.Key == "vcs.modified" {
+			if s.Value == "false" {
+				modified = false
+			}
+			break
+		}
+	}
+
+	develVersion := "devel"
+	if modified {
+		return develVersion
+	}
+	if bi.Main.Version == "" {
+		return develVersion
+	}
+	return bi.Main.Version
+}