### Is your feature request related to a problem? No ### What solution would you like? The semantic search template https://github.com/opensearch-project/flow-framework/blob/2d36058884e729352dc0504ef6bc500cff08a0c1/src/main/resources/substitutionTemplates/semantic-search-template.json hard-codes the index settings. 1. I like the simplification, and for people that are doing only vector-based semantic search this will help 2. But, if I want additional fields for any reason, or tighter control over the field definition, I can't do that. Most people doing semantic search will have other fields. The flow framework should support something like `"create_index.additional_field_definitions": Dict[str: str]` The additional fields should be added during index creation. ### What alternatives have you considered? It is possible to add the additional fields after the index is created, but that reduces the simplicity provided by the templated workflows ### Do you have any additional context? NA