DOC-2045: Add missing limits to Serverless usage limits (#518)

* DOC-2045: Add missing limits to Serverless usage limits

Add Producer IDs, Schema Registry (max schemas, max subjects, rate
limit), Connect pipelines, MCP servers, and AI agents limits to the
Serverless cluster type page.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* change Connect to Redpanda Connect

* minor edits

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: micheleRP

modules/get-started/pages/cluster-types/serverless.adoc

@@ -24,7 +24,15 @@ Each Serverless cluster has the following maximum usage limits:
 * **Users**: 30
 * **ACLs**: 120
 * **Consumer groups**: 200
-* **Connections**: 10,000 
+* **Connections**: 10,000
+* **Producer IDs**: 250
+* **Schema Registry**:
+** **Max schemas**: 500
+** **Max subjects**: 500
+** **Rate limit**: 100 requests/s
+* **Redpanda Connect pipelines**: 10
+* **MCP servers**: 10
+* **AI agents**: 10
 
 
 NOTE: The partition limit is the number of logical partitions before replication occurs. Redpanda Cloud uses a replication factor of 3.