DOCSP-15331 doc for regex pattern matching option for wildcard collections (#140)

Author: kanchana-mongodb

source/includes/atlas-config-format.json

@@ -17,7 +17,8 @@
             {
               "storeName" : "<string>",
               "database" : "<string>",
-              "collection" : "<string>" 
+              "collection" : "<string>",
+              "collectionRegex" : "<string>" 
             }
           ]
         }

source/includes/atlas-databases-config-format.json

@@ -8,7 +8,8 @@
           {
             "storeName" : "<string>",
             "database" : "<string>",
-            "collection" : "<string>"
+            "collection" : "<string>",
+            "collectionRegex" : "<string>" 
           }
         ]
       }