Add build version to NetBird client user agent. (#248)

This also fix the runtime import aliases to avoid conflicts with stdlib
runtime.

internal/version/version.go

@@ -2,6 +2,36 @@
 
 package version
 
+import (
+	"runtime/debug"
+)
+
 func ClientImage() string {
 	return "ghcr.io/netbirdio/netbird:0.70.4@sha256:3a28b9f7f32875c6a35f952ca7e9cb688b1e610365365ff55f6e790da3950f55"
 }
+
+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
+}