Allow named short urls, only allow redirects for issues made by specific user, and preview redirect (based off amcwb)

[river]

Based off amcwb's PR. Loved his ideas but the code was not working for me, so I rewrote it in a way that seems to be working now.

1. If user goes to https://domain/{TEXT} rather than https://domain/{NUMBER}, will redirect to an GH Issue that has {TEXT} as its description.
2. If user goes to https://domain/{TEXT}? will display the URL to redirect to, without actually redirecting.
3. Will not redirect of the GH Issue was not created by a specific user (specified at the config at the top).