enhancement: add "ocr_only" strategy for PDFs (#553)
* add tests for validating strategy
* refactor into determine_pdf_strategy function
* refactor pdf strategies into strategies
* remove commented out code
* remove unreachable code
* add in handling for image types
* a little more refactoring
* import ocr partioning for images
* catch warnings, partition type for valid strategies
* fallback to ocr_only from fast
* fallback logic for hi_res
* test for fallback to ocr only
* fallback logic ofr ocr_only
* more tests for fallback logic
* update doc strings
* version and changelog
* linting, linting, linting
* update docs to include notes about strategy
* fix typos
* change back patched filename
