Add param to control how model is selected in hybrid table extractor

[HenryL27]

add model param (exposed through table_extraction_options):

• if set to "tatr", will use table transformer
• if set to "deformable", will use deformable detr (ours)
• if set to an int, will use that int as the threshold
• if set to None (or unset), will use the default of 500 threshold.
• if set to anything else, error