[Backport 8.13] Add prefix strings to PUT model request (#2450)

Follow up to #2363 where prefix_strings option was added to TrainedModelConfig

(cherry picked from commit f6ec736)

Co-authored-by: David Kyle <david.kyle@elastic.co>

Author: github-actions[bot]

output/openapi/elasticsearch-serverless-openapi.json

@@ -429,9 +429,9 @@ export class TrainedModelPrefixStrings {
   /**
    * String prepended to input at ingest
    */
-  ingest: string
+  ingest?: string
   /**
    * String prepended to input at search
    */
-  search: string
+  search?: string
 }

output/schema/schema.json

@@ -22,6 +22,7 @@ import { RequestBase } from '@_types/Base'
 import { Id } from '@_types/common'
 import { long } from '@_types/Numeric'
 import { Definition, Input } from './types'
+import { TrainedModelPrefixStrings } from '../_types/TrainedModel'
 import { TrainedModelType } from '../_types/TrainedModel'
 import { InferenceConfigCreateContainer } from '@ml/_types/inference'
 
@@ -102,5 +103,11 @@ export interface Request extends RequestBase {
      * An array of tags to organize the model.
      */
     tags?: string[]
+    /**
+     * Optional prefix strings applied at inference
+     * @availability stack since=8.12.0
+     * @availability serverless
+     */
+    prefix_strings?: TrainedModelPrefixStrings
   }
 }