fix(upload/272): don't magically set filename on set file content

[shcheklein]

Fixes #272

I don't see a good reason to keep this behavior. Magic that is not consistent with other Set*Content methods.

Downside of this approach is that it breaks the compatibility a bit. Let's see how it goes, we might release a major / minor version.

---

TODO:

• [x] Add tests
• [x] Check docs and examples
• [ ] Bump at least a minor version after release since it changes the behavior a bit