Add option to change file extension from tiff to tif

[Wetzer2]

Motivation
Some tools except only "tif" as file extension. Actual chaiNNer saved TIFF files with "tiff" as file extension. This need a special step for changing the file extension to "tif".

Description
Please add an option for changing the file extension between "tiff" and "tif" in the tiff save node.

Alternatives
Creating a node to change file names incl. file extensions