Add an environment variable that allows users to send themselves tokens so that they can register an account on the instance.

Desired Outcome:

• User can generate and send their own tokens.
• User no longer has to rely on admins to generate and send them a token.

Notes:

• Due to the security risk this can possess, this feature will be made so that it can only be enabled via injecting an environment variable or modifying appsettings.json
• For hosts/instance owners, it is NOT recommended that open registration be enabled long term as malicious actors can gain access to your instance easily by registering an account and filling up your instance with spam. It is best to only enable this temporarily.