feat: allow extra config with multiple output command

[badGarnet]

This PR adds the ability to pass extra config items like generating hocr boxes when using multiple output function.

testing

• a unit test is added
• one can also locally run something like

from unstructured_pytesseract import run_and_get_multiple_output

hocr_result, text_result = run_and_get_multiple_output(images[0], extensions=["hocr", "txt"], extra_config="hocr_char_boxes=1")

then hocr_result should contain information about bounding boxes with fields \bbox

[christinestraub]

LGTM