Determine the potential \(\varphi(x, y, z)\) of an electrostatic field \(\mathbf{E}=a y \mathbf{i}+(a x+b z) \mathbf{j}+b y \mathbf{k},\) where \(a\) and \(b\) are constants, i, \(\mathbf{j}, \mathbf{k}\) are the unit vectors of the axes \(x, y, z\).