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/services/sqlstore/user.go

@@ -344,12 +344,21 @@ func GetSignedInUser(query *m.GetSignedInUserQuery) error {
 }
 
 func SearchUsers(query *m.SearchUsersQuery) error {
-	query.Result = make([]*m.UserSearchHitDTO, 0)
+	query.Result = m.SearchUserQueryResult{
+		Users: make([]*m.UserSearchHitDTO, 0),
+	}
 	sess := x.Table("user")
 	sess.Where("email LIKE ?", query.Query+"%")
-	sess.Limit(query.Limit, query.Limit*query.Page)
+	offset := query.Limit * (query.Page - 1)
+	sess.Limit(query.Limit, offset)
 	sess.Cols("id", "email", "name", "login", "is_admin")
-	err := sess.Find(&query.Result)
+	if err := sess.Find(&query.Result.Users); err != nil {
+		return err
+	}
+
+	user := m.User{}
+	count, err := x.Count(&user)
+	query.Result.TotalCount = count
 	return err
 }