Increase Marketplace image size to 5GB (#4277)

Changing os max disk size to 5000 for 5GB for Mariner 2.0 Marketplace Image

toolkit/imageconfigs/marketplace-gen2.json

@@ -2,7 +2,7 @@
     "Disks": [
         {
             "PartitionTableType": "gpt",
-            "MaxSize": 1500,
+            "MaxSize": 5000,
             "Artifacts": [
                 {
                     "Name": "cblmariner-gen2",