[skip ci] Add comment for CreateAlias (#12018)

Signed-off-by: Ndragondriver <jiquan.long@zilliz.com>

internal/proxy/impl.go

@@ -1693,6 +1693,7 @@ func (node *Proxy) Query(ctx context.Context, request *milvuspb.QueryRequest) (*
 	}, nil
 }
 
+// CreateAlias create alias for collection, then you can search the collection with alias.
 func (node *Proxy) CreateAlias(ctx context.Context, request *milvuspb.CreateAliasRequest) (*commonpb.Status, error) {
 	if !node.checkHealthy() {
 		return unhealthyStatus(), nil