Rename DefaultPageSize => PagerSize

This was recently introduced. so no breaking change.

The thing is:

* We do not commonly use the prefix Default* even if it can be overridden in the templates.
* PagerSize makes more sense and is also the term used in the code.

config/commonConfig.go

@@ -413,8 +413,8 @@ func DecodeServer(cfg Provider) (Server, error) {
 
 // Pagination configures the pagination behavior.
 type Pagination struct {
-	//  Default number of elements per page in pagination.
-	DefaultPageSize int
+	//  Default number of elements per pager in pagination.
+	PagerSize int
 
 	// The path element used during pagination.
 	Path string