Added tags with ordering index (#318)

Co-authored-by: Aaron Stannard <[email protected]>

Author: Peter Huang

src/Akka.Persistence.MongoDb/Journal/MongoDbJournal.cs

@@ -97,6 +97,15 @@ protected override void PreStart()
 
                     collection.Indexes
                         .CreateOne(modelWithOrdering);
+
+                    var tagsWithOrdering = new CreateIndexModel<JournalEntry>(
+                       Builders<JournalEntry>
+                           .IndexKeys
+                           .Ascending(entry => entry.Tags)
+                           .Ascending(entry => entry.Ordering));
+
+                    collection.Indexes
+                        .CreateOne(tagsWithOrdering);
                 }
 
                 return collection;