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.

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TODO:

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