Mark the Central configuration for EDOT SDKs doc as unavailable on Serverless (#499)

Marks the Central configuration for EDOT SDKs doc as unavailable on Serverless

Author: vishaangelova

docs/reference/central-configuration.md

@@ -5,6 +5,7 @@ applies_to:
   deployment:
       ess: preview 9.1
   stack: preview 9.1
+  serverless: unavailable
 products:
   - id: observability
   - id: kibana