Fix MultiSearch functionality (#8176)

- Implement `IStreamSerializable` for array request descriptors
- Do not automatically infer index for optional `Indices` parameters

Author: flobernd

src/Elastic.Clients.Elasticsearch.Serverless/_Generated/Api/AsyncSearch/SubmitAsyncSearchRequest.g.cs

@@ -958,7 +958,7 @@ public SubmitAsyncSearchRequestDescriptor(Elastic.Clients.Elasticsearch.Serverle
 	{
 	}
 
-	public SubmitAsyncSearchRequestDescriptor() : this(typeof(TDocument))
+	public SubmitAsyncSearchRequestDescriptor()
 	{
 	}
 

src/Elastic.Clients.Elasticsearch.Serverless/_Generated/Api/Cluster/HealthRequest.g.cs

@@ -186,7 +186,7 @@ public HealthRequestDescriptor(Elastic.Clients.Elasticsearch.Serverless.Indices?
 	{
 	}
 
-	public HealthRequestDescriptor() : this(typeof(TDocument))
+	public HealthRequestDescriptor()
 	{
 	}