Paperpile-notion

Caught a bug that would keep BibTeX from properly loading.

Fixes a few quirks with the GitHub Action, ensure a consistent `config.yaml` (it was outdated), and allow some more fields in the `config.yaml` to be optional.

Migrates from JSON to BibTeX support, as Paperpile's Workflows strictly support BibTeX exports. Adds `paperpile-notion` as a GitHub action. Check out the [jmuchovej/sync-paperpile-to-notion][tpl] Template Repository to setup your syncing between Paperpile and Notion.

[tpl]: https://github.com/jmuchovej/sync-paperpile-to-notion

Adds color formatting. Removes `tqdm` progress bar (`click` compatibility issue).

Functionally equivalent to `0.1.0`, cleans up `config.yaml` syncing.