Add a CLI option to select reader to use

[mwestphal]

Is your feature request related to a problem? Please describe.
F3D rely on file extension to detect which reader to use, but sometimes this detection is not enough. Moreover, F3D can have multiple readers for the same extension, in that case it is not possible to choose which one to use.

Describe the solution you'd like

• Add a CLI option to select the reader to use based on its name.
• Pass this option to the reader selection mechanism to force it
• Add a test, the draco/gltf readers are a possible candidate for testing this