Indices should always be loaded in the same order

I run into a situation where rails application server loaded indices in a different order than they were indexed in (on a different server). That broke index offset calculation. See:

Rails app server
```
irb(main):001:0> Dir["app/indices/**/*.rb"]
=> ["app/indices/knowledge_base_topic_index.rb", "app/indices/chat_message_index.rb", "app/indices/ticket_index.rb"]
```
offsets:
```
0 -> knowledge_base_topics
1 -> chat_messages
2 -> tickets
```

Util server (used for indexing)
```
irb(main):001:0> Dir["app/indices/**/*.rb"]
=> ["app/indices/knowledge_base_topic_index.rb", "app/indices/ticket_index.rb", "app/indices/chat_message_index.rb"]
```
offsets:
```
0 -> knowledge_base_topics
1 -> tickets
2 -> chat_messages
```