Tested in combination with the rest of the stack as follows:
1. Override `defaultURLPrefix` in `native/utils/url-utils.js` to return some random string. This makes sure that the "default" of Ashoat's keyserver does not work, and makes it so the re
gistration flow only works if the user selects a custom keyserver and all of the server calls in the registration flow use that custom keyserver
2. Test the registration flow end-to-end for an Ethereum account
3. Test the registration flow end-to-end for a username/password account
4. Test the registration flow end-to-end for a username/password account with a custom avatar that requires an image upload
5. Make sure that for all registrations, the correct avatar appears in the `ChatThreadList` when the `RegistrationNavigator` dismisses