seeds: Add testnet4 fixed seeds file

Author: achow101

contrib/seeds/nodes_testnet4.txt

@@ -0,0 +1,9 @@
+18.189.156.102:48333 # AS16509
+18.201.207.55:48333 # AS16509
+51.158.248.8:48333 # AS12876
+57.128.176.163:48333 # AS8220
+82.67.102.15:48333 # AS12322
+88.99.248.50:48333 # AS24940
+95.217.73.162:48333 # AS24940
+103.99.171.212:48333 # AS54415
+103.165.192.210:48333 # AS54415