This really depends on what type of apartment you want to rent out. Tenants in an affordable 1-room apartment in Neukölln, for example, will be happy to find a dishwasher but they don’t expect it. But for higher-priced apartments, it is a different matter. For a lot of working people, a dishwasher is a must-have and beyond a particular rental price, it is also expected to be there.
But even if you are renting out your apartment in a lower price range, it is worthwhile to think about installing a dishwasher. It of course saves more energy than hand washing the dishes and morever you will avoid finding your dishes and cutlery in a dirty state after the tenant moves out. Even the next tenant, or whoever does the final cleaning, will be grateful to you.