Creating a usb charger from 2 wire DC
Yuck, Apple charging.
The configuration of resistors on the data lines you need for this is proprietary (a polite way of saying &quot;customer lock-in&quot;) Apple and will not only depend on the type of Apple device (IPhone, IPad, IPod), but also on its generation, and possibly on the phase of the moon at the time of manufacture.
What you want is doable, but I don't know about an off-the-shelf solution you can just connect to the end of your wire.
There are a few articles on the on the interwebs, like here and here, that show different resistor configurations for wiring things up yourself, but you have to be careful to check if they apply for your specific generation of IPad, and test before you install.
You could try, as an experiment, shorting the D+ and D- and otherwise leave them floating, and see how much current, if any, the IPad pulls when charging. If it works, and the charging current is enough to keep the IPad running when connected to its charger continuously, you're done.
You can probably google the exact required resistors and connections needed to comply with the IPad's demands, but to be honest, I would just get a charger that is known to work well with your IPad and wire that in place, USB cable and all.