GCP limit can probably raised from 7000 to 10000

There is a limit of 7000 GCPs enforced here: https://github.com/GFZ/arosics/blob/8daeb821340c1dad3dafb2d0a78c16a0dcff82a4/arosics/Tie_Point_Grid.py#L755

This can probably raised safely to 10000.

The reason for this limit is apparently the size limit in bytes of the TIFF tag (!): https://gis.stackexchange.com/questions/343408/is-there-a-limit-to-the-number-of-gcps-that-can-be-used