android: persist Amplitude device id when not set externally

Co-authored-by: Titus-Andrei Moldovan <moldovan.titus@gmail.com>

android/sdk/src/main/java/org/jitsi/meet/sdk/AmplitudeModule.java

         String android_id = sharedPreferences.getString(AMPLITUDE_DEVICE_ID_KEY, "");
         if (!TextUtils.isEmpty(android_id)) {
             Amplitude.getInstance(instanceName).setDeviceId(android_id);
+        } else {
+            String amplitudeId = Amplitude.getInstance(instanceName).getDeviceId();
+            SharedPreferences.Editor editor = sharedPreferences.edit();
+            editor.putString(JITSI_PREFERENCES, amplitudeId).apply();
         }
     }