Allow Hypernet previews to create_infotext.

[timntorres]

As per #2921, Hypernet preview images now support infotext if the user so desires.

Tested and works with... ✅ ...both enabled and disabled checkbox “Read parameters (prompt, etc...) from txt2img tab when making previews.” ✅ ...both enabled and disabled checkbox “Create a text file next to every image with generation parameters.” ✅ ...both enabled and disabled checkbox “Save text information about generation parameters as chunks to png files." ✅ ...every permutation of those settings.

Additional thoughts: Although this implementation does not list the exact checkpoint; each image itself is named after that checkpoint, so the user should have no trouble finding it. Besides, even if it were to list the generation's closest checkpoint, the user will not yet have placed that checkpoint into the hypernetwork folder anyway, and so attempting to send the PNG info anywhere would cause the hypernetwork to unload entirely.

Appending the checkpoint to the Hypernet name in processing.py (via shared.loaded_hypernetwork?) seems like it'll require some nontrivial refactoring, though, so I will study more before attempting to implement it myself. Once added, though, it might be useful for the program to copy that relevant checkpoint to the hypernetwork folder on its own instead of unloading.