Allow specifying custom extension in create_file

[gergesh]

[Zachatoo]

Thanks for contributing!

Can you help me understand the use case? I believe tp.file.create_new should work as is when referencing a template file that is of any file type, without having to explicitly define the extension.

[gergesh]

To be specific on my usage: I'm simply trying to create a new file with a custom extension from a template script.