Revert "Uppercase enum source mode" (#3810) (#3843)

* Revert "Switch enums from upper case to lower case"

(cherry picked from commit 779fb2a)

Co-authored-by: Quentin Pradet <[email protected]>
Co-authored-by: Laura Trotta <[email protected]>

Author: 3 people

output/openapi/elasticsearch-openapi.json

@@ -501,9 +501,9 @@ export class MappingLimitSettingsSourceFields {
 }
 
 export enum SourceMode {
-  DISABLED,
-  STORED,
-  SYNTHETIC
+  disabled,
+  stored,
+  synthetic
 }
 
 export class SlowlogSettings {