Run script to find list of specs periodically

[tidoust]

See discussion in #70 (comment)

Goal is to set up a regular GitHub action to run the script that finds new specs periodically (once per week?), and have it raise a GitHub issue with new specs it may find.

Note that the action should also check lastreviewed dates in monitor-repos.json and force a periodic review for entries that have not been checked in the last 3 months or so.

[dontcallmedom]

implemented in #76