[NET-3700] add `omitempty` to api prepared query targets (#18184)

add `omitempty` to api prepared query targets

Manual backport of c2bbe67714.

Co-authored-by: Nick Irvine <115657443+nfi-hashicorp@users.noreply.github.com>

api/prepared_query.go

@@ -32,11 +32,11 @@ type QueryFailoverTarget struct {
 
 	// Partition specifies a partition to try during failover
 	// Note: Partition are available only in Consul Enterprise
-	Partition string
+	Partition string `json:",omitempty"`
 
 	// Namespace specifies a namespace to try during failover
 	// Note: Namespaces are available only in Consul Enterprise
-	Namespace string
+	Namespace string `json:",omitempty"`
 }
 
 // QueryDNSOptions controls settings when query results are served over DNS.