Add > 50 stars criteria to feeling-lucky

In testing https://github.com/bnb/good-first-issue/pull/57, I noticed that 5 of the first 7 runs of the `good-first-issue feeling-lucky` command were all repos with only a few issues and two of them were total spam issues created within the last day.

To help ensure that we're _actually_ sending users to Good First Issues that they'll be able to make a meaningful contribution to, how do we feel about setting a filter for ⭐️s to 50?

If we want to ensure that there's still a way to pull from the full set of "Good First Issues" I'd not be opposed to adding an "All" command in the same release that the filter is shipped.