Add stale repos workflow

[Firebird1029]

Add stale repos workflow

Problem

Currently, there is no way to easily see which repos in the DSACMS org
are stale.

Solution

This Github Action workflow automatically creates an issue in the open
repo with a list of stale repos in the DSACMS Github org. The workflow
is currently configured to run on the first day of every month, and is set
to recognize stale repos when they reach over one year without
any edits.

Result

The automated issue it created is here: #41

[decause-gov]

Very interesting!

A couple of thoughts/questions:

1. Should we broaden the staleness threshhold to 730 days? (2 years?) Public Sector repos tend to go through longer cycles of dormancy, based on what we've seen so far.
2. Should this run in /metrics instead of /open?
3. Should this feed metadata in our code.json file? (lastUpdated perhaps?)
   3a. There is also metadata for (createdAt, and latestRelease, iirc?) Should we lump them all into one workflow/script?

I think there's no harm in shipping this as is, but I think we want /metrics code.json/repometrics to be our 'source of truth' for metadata about repos going forward.

[Firebird1029]

Created new PR in metrics repo.