[client] Implement environment variable handling for Android (#4440)

Some features can only be manipulated via environment variables. With this PR, environment variables can be managed from Android.

client/android/env_list.go

@@ -0,0 +1,32 @@
+package android
+
+import "github.com/netbirdio/netbird/client/internal/peer"
+
+var (
+	// EnvKeyNBForceRelay Exported for Android java client
+	EnvKeyNBForceRelay = peer.EnvKeyNBForceRelay
+)
+
+// EnvList wraps a Go map for export to Java
+type EnvList struct {
+	data map[string]string
+}
+
+// NewEnvList creates a new EnvList
+func NewEnvList() *EnvList {
+	return &EnvList{data: make(map[string]string)}
+}
+
+// Put adds a key-value pair
+func (el *EnvList) Put(key, value string) {
+	el.data[key] = value
+}
+
+// Get retrieves a value by key
+func (el *EnvList) Get(key string) string {
+	return el.data[key]
+}
+
+func (el *EnvList) AllItems() map[string]string {
+	return el.data
+}