Add issue open date and the last date the repository had commits to the display

[benfulton]

To help users distinguish between projects that are active and those that have gone cold, it would be useful to show the date that the issue was opened, and the last time the repository itself was updated.

[vsoch]

To play devil's advocate, a lot of good first issues are open a long time, and not because the project isn't interested, but because they can't find someone to work on them. So my 0.02 would be that the projects (repos) we add should generally be curated, and leave the filtering / removal of old issues up to them.

[vsoch]

But if you feel strongly about this, here is where in the action you should add the metadata: https://github.com/rseng/good-first-issues/blob/73ba97eeb57a7f1eef072ced8d5abb919e8b6774/scripts/generate-first-issues.py#L88-L94 pull requests are welcome! And then we would update the version here.