Apple Inc. is launching a new product-insurance plan that bundles coverage for as many as three devices, part of a broader effort to drum up subscription revenue.The new offering is called AppleCare One and costs $20 a month, the company said Wednesday. The service also includes battery replacements, all-hours customer support and coverage for accidental damage, such as drops and spills. Any additional products added to the plan will cost an extra $6 a month....