Update documentation on writing new samples

With all those recent changes and improvements to the framework, esp. in regards to unifying the C/C++bindings, we should update and extend our documentation for writing new samples. This also includes the sample templates.

That way we can ensure that maintainers write code the way we intend.

Start by locating the documentation for writing new samples and the sample templates, then compare them with the recent C/C++ binding changes mentioned in the issue. Done means the guidance and templates consistently describe the intended maintainer conventions for new samples.

Written by the indexing model from the issue text.