Fixed "no such group" error in Dockerfile, added docx2txt and cryptography deps

[dividebysandwich]

Creating a docker container was giving me a "No such group" error for the worker group. This has been fixed. Also, I have added docx2txt to poetry, so users no longer get the error that docx2txt is not installed when running privategpt in a docker container. cryptography has been added as well to remove the error when trying to parse certain PDF files.