Added namespaceValidator check to IndexService.parseRuntimeMappings

This prevents _project or _project.foo mappings in query-time runtime mappings.

For example, these now fail with "Mapping rejected: [_project.foo]. No mappings of [_project] are allowed in order to avoid conflicts with project metadata tags in serverless"
GET /blogs/_search
{
  "runtime_mappings": {
    "_project": {
      "type": "keyword",
      "script": {
        "source": "emit('somevalue')"
      }
    }
  },
  "query": {
    "match_all": {}
  },
  "fields": ["_project"]
}

GET /blogs/_search
{
  "runtime_mappings": {
    "_project.foo": {
      "type": "keyword",
      "script": {
        "source": "emit('somevalue')"
      }
    }
  },
  "query": {
    "match_all": {}
  },
  "fields": ["_project.foo"]
}

Author: quux00

server/src/main/java/org/elasticsearch/index/IndexService.java

@@ -1409,6 +1409,11 @@ public static Map<String, MappedFieldType> parseRuntimeMappings(
         // TODO add specific tests to SearchExecutionTests similar to the ones in FieldTypeLookupTests
         MappingParserContext parserContext = mapperService.parserContext();
         Map<String, RuntimeField> runtimeFields = RuntimeField.parseRuntimeFields(new HashMap<>(runtimeMappings), parserContext, false);
+        if (parserContext.getNamespaceValidator() != null) {
+            for (String runtimeFieldName : runtimeFields.keySet()) {
+                parserContext.getNamespaceValidator().validateNamespace(null, runtimeFieldName);
+            }
+        }
         Map<String, MappedFieldType> runtimeFieldTypes = RuntimeField.collectFieldTypes(runtimeFields.values());
         if (false == indexSettings.getIndexMetadata().getRoutingPaths().isEmpty()) {
             for (String r : runtimeMappings.keySet()) {