Referral program

[MauAraujo]

POR-

What does this PR do?

This PR adds a referral program for granting certain credits to users who refer 5 other users.

It includes a lot of boilerplate code, but the most important parts for reviewing are:

• New ReferralsPage in the dashboard
• Moved all credit specific endpoints to credits.go handler
• When creating a user, a random referral code is generated for them
• Users are able to use a referral link for the register page with the referral code
• Users can claim their reward once across projects once they meet the conditions