Feature request: Notmuch integration

[Notmuch] is a tag-based indexer and email system which can run locally.

Similarly to how tasks can be created from Gmail labels, it would be nice to
allow tasks to be created from Notmuch tags.

For this, some integration could be created based on some existing [Python
bindings].

[Notmuch]: https://notmuchmail.org/
[Python bindings]: https://notmuchmail.org/doc/latest/python-bindings.html