The mosaic flag must be false by default when a zip with a Geotiff is uploaded

[giohappy]

When a zip containing a Geotiff dataset is uploaded we get the following error:

Could not find any valid Time Regex for the Mosaic files.
Traceback (most recent call last):
  File "/mnt/c/Work/Code/geonode/geonode/upload/views.py", line 705, in view
    resp = _steps[step](req, upload_session)
  File "/mnt/c/Work/Code/geonode/geonode/upload/views.py", line 161, in save_step_view
    import_session, upload = save_step(
  File "/usr/lib/python3.8/contextlib.py", line 75, in inner
    return func(*args, **kwds)
  File "/mnt/c/Work/Code/geonode/geonode/upload/upload.py", line 427, in save_step
    raise e
  File "/mnt/c/Work/Code/geonode/geonode/upload/upload.py", line 340, in save_step
    target_store, files_to_upload = utils.import_imagemosaic_granules(
  File "/mnt/c/Work/Code/geonode/geonode/upload/utils.py", line 722, in import_imagemosaic_granules
    raise GeneralUploadException(detail=_("Could not find any valid Time Regex for the Mosaic files."))
geonode.upload.api.exceptions.GeneralUploadException: Could not find any valid Time Regex for the Mosaic files.
Internal Server Error: /api/v2/uploads/upload
"POST /api/v2/uploads/upload HTTP/1.1" 500 114

Probably due to the processing of the mosaic field

The upload must set the default value for mosaic to False, without expecting the client to set it.

[giohappy]

is this still valid @afabiani?