Ocr patterns

Adds support for passing tesseract configuration, including specifying custom dictionaries and patterns.

Notes:

* Tesseract pattern language is nasty and unfortunately doesn't easily map to regex or other similar.

TODO:

- [x] Add more tests
- [x] Add example usage
- [x] Make patterns work with multiple languages
- [x] Squash Dave's fixups into other commits
- [x] Fix commit message of "Refactor: _tesseract: Allow passing a `Gst.Sample` as frame …" to fit better with this commit series
- [x] The commit message of "OCR: Add ability to pass configuration to tesseract..." has an unfinished sentence