[APM] Add name to Observer type (elastic#72110)

Backport elastic#72078 is failing because of the type check because `observer.name` is not defined. Not sure why this wasn't a problem on master, but adding it here so I can include it.

x-pack/plugins/apm/typings/es_schemas/raw/fields/observer.ts

@@ -5,6 +5,7 @@
  */
 
 export interface Observer {
+  name?: string;
   version: string;
   version_major: number;
 }