I'm not aware of any such app and I don't see one that does this with a quick Google search. Is there a reason you're not just sharing the image directly?
That is what the share function does, when you choose to share to an external location. If you have the imgur app, you can choose it as a destination from the share menu and it will upload it.
Imgur was only an example. I don't want to use imgur's app and there are other websites or apps that I would like to upload to that do not work in that way.
I just want to be able to select an image from my clipboard when an app wants me to select an image from my phone.