The electric field due to a point charge located at the origin in \(\mathbf{R}^{3}\) is \(\mathbf{E}=k \frac{\mathbf{e}_{r}}{r^{2}}\), where \(r=\sqrt{x^{2}+y^{2}+z^{2}}\) and \(k\) is a constant. Calculate the flux of \(\mathbf{E}\) through the disk \(D\) of radius 2 parallel to the \(x y\)-plane with center \((0,0,3)\).