Make user "registration source" information more prominent and searchable

[GUI]

When agencies embed the API key signup form on, we collect a "registration source" to help identify where the user signed up from. We've had a request to make this a little more visible and searchable so it's easier to find the users that signed up from your specific agency's website.

[GUI]

It's nothing fancy, but I took an extremely simple first pass at this by including it in the main table page that lists the users (so it's more visible), and also including that field in our free-form text search on the page: NREL/api-umbrella-web@a653afe