Removing fitshape as a required argument in PSF photometry fitting, allowing default shape?

[Onoddil]

Currently fitshape is a required input into PSF fitting routines like BasicPSFPhotometry. It might be good if this could be relaxed to allow for a None parameter, for example, which simply represented "fit the entire image".

Is this a required keyword to avoid accidental huge-image-fitting runtime problems? Perhaps a warning could be raised if data.shape is above some sensible size? You'd also have to worry about even-sized images I suppose.

The use-case motivating this is previously extracted small cutouts of stars -- such as can be obtained from extract_stars -- require the computation of the cutout shapes which are then manually passed back into the PSF fitting process, which feels unnecessary when you could just use the entire cutout image to fit by default.

However, as I've basically argued against my own point above slightly this might cause more problems than it solves (given that it only solves a minor inconvenience and might create bigger issues), so feel free to reject & close this issue if it isn't worth the additional potential headaches...