Update Vertex AI fields to snake case in pipeline

packages/gcp_vertexai/changelog.yml

@@ -1,6 +1,9 @@
 # newer versions go on top
 - version: "1.4.0-next"
   changes:
+    - description: Update the mapping to snake case in pipeline.
+      type: enhancement
+      link: https://github.com/elastic/integrations/pull/15604
     - description: Add support for Vertex AI Prompt Response Logs datastream.
       type: enhancement
       link: https://github.com/elastic/integrations/pull/15435

packages/gcp_vertexai/data_stream/prompt_response_logs/elasticsearch/ingest_pipeline/default.yml

@@ -37,7 +37,41 @@ processors:
       field: event.action
       copy_from: gcp.vertexai.prompt_response_logs.api_method
       if: ctx.gcp?.vertexai?.prompt_response_logs?.api_method != null
-
+
+  # Rename camelCase fields to snake_case
+
+  - script:
+      lang: painless
+      source: |
+        Map keysToSnakeCase(Map m) {
+            def regex = /_?([a-z])([A-Z]+)/;
+            def snakeCaseMap = [:];
+            for (entry in m.entrySet()) {
+            def k = entry.getKey();
+            def v = entry.getValue();
+            if (v instanceof Map) {
+                v = keysToSnakeCase(v);
+            } else if (v instanceof List) {
+                for (int i = 0; i < v.size(); i++) {
+                def item = v.get(i);
+                if (item instanceof Map) {
+                    v.set(i, keysToSnakeCase(item));
+                }
+                }
+            }
+            k = regex.matcher(k).replaceAll('$1_$2').toLowerCase();
+            snakeCaseMap.put(k, v);
+            }
+            return snakeCaseMap;
+        }
+
+        if (ctx.gcp?.vertexai?.prompt_response_logs?.full_request != null) {
+            ctx.gcp.vertexai.prompt_response_logs.full_request = keysToSnakeCase(ctx.gcp.vertexai.prompt_response_logs.full_request);
+        }
+        if (ctx.gcp?.vertexai?.prompt_response_logs?.full_response != null) {
+            ctx.gcp.vertexai.prompt_response_logs.full_response = keysToSnakeCase(ctx.gcp.vertexai.prompt_response_logs.full_response);
+        }
+
 
   # Remove null and empty values recursively
   - script: