[BUG] data-prepper sink fails to create templates when `number_of_shards` is passed

Describe the bug
I have data-prepper creating templates and sending data with no issue
This is the config

          sink:
            - opensearch:
                hosts: ["$${OS_HOST}"]
                username: $${OS_USER}
                password: $${OS_PASS}
                index_type: trace-analytics-raw
                template_type: index-template
                max_retries: 10

My cluster sets the number of shards=5 as the default value for new indices being rolled over.
So, I tried adding an extra line to change that settings as stated here in the docs

number_of_shards: 1

But as soon I restart the service it starts to fail with the following error

Request failed: [x_content_parse_exception] [1:1118] [index_template] unknown field [settings]

To Reproduce
Steps to reproduce the behavior:

1. Set a sink to use OpenSearch as shown above using number_of_shards: N
2. Restart the service

Expected behavior
Templates should be created using the right sharding number.

Environment (please complete the following information):

• Amazon OpenSearch service
• Version [2.11]

Start with the OpenSearch sink configuration and the template-creation path, using the reproduction configuration with number_of_shards set. Reproduce the index-template error against OpenSearch 2.11, then verify that templates are created successfully with the requested shard count.