Add vpn start attempt success pixels (#4633)

Task/Issue URL:
https://app.asana.com/0/1203137811378537/1207529492824734/f

### Description
Add missing success pixels

### Steps to test this PR
QA-optional

Author: karlenDimla

app-tracking-protection/vpn-impl/src/main/java/com/duckduckgo/mobile/android/vpn/pixels/DeviceShieldPixelNames.kt

@@ -224,6 +224,7 @@ enum class DeviceShieldPixelNames(override val pixelName: String, val enqueue: B
 
     VPN_MOTO_G_FIX_DAILY("m_vpn_ev_moto_g_fix_d", enqueue = true),
     VPN_START_ATTEMPT("m_vpn_ev_start_attempt_c", enqueue = true),
+    VPN_START_ATTEMPT_SUCCESS("m_vpn_ev_start_attempt_success_c", enqueue = true),
     VPN_START_ATTEMPT_FAILURE("m_vpn_ev_start_attempt_failure_c", enqueue = true),
     ;
 }

app-tracking-protection/vpn-impl/src/main/java/com/duckduckgo/mobile/android/vpn/pixels/DeviceShieldPixels.kt

@@ -361,6 +361,8 @@ interface DeviceShieldPixels {
     fun reportMotoGFix()
 
     fun reportVpnStartAttempt()
+
+    fun reportVpnStartAttemptSuccess()
 }
 
 @ContributesBinding(AppScope::class)
@@ -774,6 +776,10 @@ class RealDeviceShieldPixels @Inject constructor(
         firePixel(DeviceShieldPixelNames.VPN_START_ATTEMPT)
     }
 
+    override fun reportVpnStartAttemptSuccess() {
+        firePixel(DeviceShieldPixelNames.VPN_START_ATTEMPT_SUCCESS)
+    }
+
     private fun suddenKill() {
         firePixel(DeviceShieldPixelNames.ATP_KILLED)
     }

app-tracking-protection/vpn-impl/src/main/java/com/duckduckgo/mobile/android/vpn/service/TrackerBlockingVpnService.kt

@@ -393,6 +393,8 @@ class TrackerBlockingVpnService : VpnService(), CoroutineScope by MainScope(), V
             stopVpn(VpnStopReason.ERROR, true)
         }
 
+        deviceShieldPixels.reportVpnStartAttemptSuccess()
+
         // This is something temporary while we confirm whether we're able to fix the moto g issues with appTP
         // see https://app.asana.com/0/488551667048375/1203410036713941/f for more info
         tunnelConfig?.let { config ->