Add GetUsersQty function to retrieve the total number of users

internal/service/users/get_users_qty.go

@@ -0,0 +1,7 @@
+package users
+
+import "context"
+
+func (s *Service) GetUsersQty(ctx context.Context) (int64, error) {
+	return s.dbgen.UsersServiceGetUsersQty(ctx)
+}

internal/service/users/get_users_qty.sql

@@ -0,0 +1,2 @@
+-- name: UsersServiceGetUsersQty :one
+SELECT COUNT(*) FROM users;