Add lektor-scss plugin per TPA-RFC-29

Context: #27 (closed) and https://gitlab.torproject.org/tpo/tpa/team/-/wikis/policy/tpa-rfc-29-lektor-scss-plugin

This package is an sdist built from the lektor-scss 1.4.1 tag using Python 3.8.13 to be compatible with our python3.8 lektor requirement. I've already vetted the plugin's safety for the RFC.

assigned to @kez

Closes #27 (closed)

@anarcat or @lavamind could you approve this tomorrow when you get a chance?

approved this merge request

lgtm

mentioned in commit 5ed7972d

merged

mentioned in merge request !59 (merged)

mentioned in issue #57 (closed)