[misc] Move shared components to shared directory (#4286)

Moved the following directories:

```
  - management/client → shared/management/client
  - management/domain → shared/management/domain
  - management/proto → shared/management/proto
  - signal/client → shared/signal/client
  - signal/proto → shared/signal/proto
  - relay/client → shared/relay/client
  - relay/auth → shared/relay/auth
```

and adjusted import paths

shared/signal/client/mock.go

@@ -0,0 +1,84 @@
+package client
+
+import (
+	"context"
+
+	"github.com/netbirdio/netbird/shared/signal/proto"
+)
+
+type MockClient struct {
+	CloseFunc                    func() error
+	GetStatusFunc                func() Status
+	StreamConnectedFunc          func() bool
+	ReadyFunc                    func() bool
+	WaitStreamConnectedFunc      func()
+	ReceiveFunc                  func(ctx context.Context, msgHandler func(msg *proto.Message) error) error
+	SendToStreamFunc             func(msg *proto.EncryptedMessage) error
+	SendFunc                     func(msg *proto.Message) error
+	SetOnReconnectedListenerFunc func(f func())
+}
+
+// SetOnReconnectedListener sets the function to be called when the client reconnects.
+func (sm *MockClient) SetOnReconnectedListener(_ func()) {
+	// Do nothing
+}
+
+func (sm *MockClient) IsHealthy() bool {
+	return true
+}
+
+func (sm *MockClient) Close() error {
+	if sm.CloseFunc == nil {
+		return nil
+	}
+	return sm.CloseFunc()
+}
+
+func (sm *MockClient) GetStatus() Status {
+	if sm.GetStatusFunc == nil {
+		return ""
+	}
+	return sm.GetStatusFunc()
+}
+
+func (sm *MockClient) StreamConnected() bool {
+	if sm.StreamConnectedFunc == nil {
+		return false
+	}
+	return sm.StreamConnectedFunc()
+}
+
+func (sm *MockClient) Ready() bool {
+	if sm.ReadyFunc == nil {
+		return false
+	}
+	return sm.ReadyFunc()
+}
+
+func (sm *MockClient) WaitStreamConnected() {
+	if sm.WaitStreamConnectedFunc == nil {
+		return
+	}
+	sm.WaitStreamConnectedFunc()
+}
+
+func (sm *MockClient) Receive(ctx context.Context, msgHandler func(msg *proto.Message) error) error {
+	if sm.ReceiveFunc == nil {
+		return nil
+	}
+	return sm.ReceiveFunc(ctx, msgHandler)
+}
+
+func (sm *MockClient) SendToStream(msg *proto.EncryptedMessage) error {
+	if sm.SendToStreamFunc == nil {
+		return nil
+	}
+	return sm.SendToStreamFunc(msg)
+}
+
+func (sm *MockClient) Send(msg *proto.Message) error {
+	if sm.SendFunc == nil {
+		return nil
+	}
+	return sm.SendFunc(msg)
+}