Add Northern Russia campaign.

https://github.com/dcs-liberation/dcs_liberation/issues/1202

resources/campaigns/northern_russia.json

@@ -0,0 +1,11 @@
+{
+  "name": "Caucasus - Northern Russia",
+  "theater": "Caucasus",
+  "authors": "Plob",
+  "recommended_player_faction": "USA 2005",
+  "recommended_enemy_faction": "Russia 1990",
+  "description": "<p>A medium campaign through the north eastern part of the Caucasus map.</p><p>Russia has invaded Georgia through the eastern mountains. Mount a counter offense and push them back!",
+  "miz": "northern_russia.miz",
+  "performance": 2,
+  "version": "6.0"
+}