Magnetic anisotropy energies and metal-insulator transitions in monolayers of <math> <mrow> <mi>α</mi> <mtext>−</mtext> <msub> <mi>RuCl</mi> <mn>3</mn> </msub> </mrow> </math> and <math> <msub> <mi>OsCl</mi> <mn>3</mn> </msub> </math> on graphene