Clarafies Logpush datasets availability (#18348)

Author: angelampcosta

src/content/docs/logs/reference/log-fields/index.mdx

@@ -25,6 +25,7 @@ The `<DATASET>` argument indicates the log category. For example, `http_requests
 
 ## Availability
 
+* The availability of Logpush dataset fields depends on your subscription plan.
 * Zone-scoped HTTP requests are available in both Logpush and Logpull.
 * [Custom fields](/logs/reference/custom-fields/) for HTTP requests are only available in Logpush.
 * All other datasets are only available through Logpush.