admin: adds paging to global user list

Currently there is a limit of 1000 users in the global
user list. This change introduces paging so that an
admin can see all users and not just the first 1000.

Adds a new route to the api - /api/users/search that
returns a list of users and a total count. It takes
two parameters perpage and page that enable paging.

Fixes #7469

pkg/models/user.go

@@ -130,7 +130,14 @@ type SearchUsersQuery struct {
 	Page  int
 	Limit int
 
-	Result []*UserSearchHitDTO
+	Result SearchUserQueryResult
+}
+
+type SearchUserQueryResult struct {
+	TotalCount int64               `json:"totalCount"`
+	Users      []*UserSearchHitDTO `json:"users"`
+	Page       int                 `json:"page"`
+	PerPage    int                 `json:"perPage"`
 }
 
 type GetUserOrgListQuery struct {