[feat] add marker strategy as a separate repo + example how to load it

As with the #91 - the `marker` strategy has been officially removed along with all dependencies to `surya-ocr` and `marker` - as the packages imply the `GPL3` license. We changed the license to MIT. `marker`, `surya`, `tabled` and other GPL licensed products still might be used BUT only as a 3rd party libraries - included at the local-deployment level and not in the core product.

Looking forward for someone willing to add it as a 3rd party plugin/example