[BUG] Index setting partition size is ignored if routing num shard setting is not specified, leading to ingestion to single shard

[MilanCoder]

Describe the bug

Hi,

We came up with an issue in opensearch 2.11 where while ingesting data into an index, all the data was getting routed to single shard even if we specify the partition size to more than 1 as value, it seems the data was only getting distributed to multiple shards if we specify the routing num shards setting value to equal to num of shards.

Setting used without routing num shards setting :

` "settings": {
      "number_of_shards": 20,
      "index.routing_partition_size": 3,
      "number_of_replicas": 0,
      "refresh_interval": "300s"
  },`

Setting used with routing num shards setting which works as expected.

 "settings": {
      "number_of_shards": 20,
      "index.routing_partition_size": 3,
      "number_of_replicas": 0,
      "refresh_interval": "300s",
      "number_of_routing_shards":20
  },

Related component

No response

To Reproduce

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

It should work without specifying routing num shards setting. The data should get distributed across shards.

Additional Details

Plugins
Please list all plugins currently enabled.

Screenshots
If applicable, add screenshots to help explain your problem.

Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.