Allow Custom URL Schemas in OAuth Client Redirect

[spencerrlongg]

Laravel's standard url validation rule only deals with the http,https schemas. You can define more schemas in it, for instance url:http,https,com.grokability.snipeitmobile but then we're only allowing our own custom schema, so I went ahead and just changed it to string - I can't think of a way this could bite us, but if you can definitely let me know and I can look into other options.

[snipe]

We could maybe make that an env var array?