Add pagination to user search endpoint

Supports offset pagination, per the docs: https://developer.zendesk.com/api-reference/ticketing/users/users/#search-users

zendesk/user.go

@@ -106,6 +106,7 @@ type UserRelated struct {
 //
 // ref: https://developer.zendesk.com/api-reference/ticketing/users/users/#search-users
 type SearchUsersOptions struct {
+	PageOptions
 	ExternalIDs string `json:"external_ids,omitempty" url:"external_ids,omitempty"`
 	Query       string `json:"query,omitempty" url:"query,omitempty"`
 }