Modify `SIWEPanel` to hit the `siwe_auth` endpoint instead of the `create_account` endpoint once SIWE message is signed.
We also modify the `SIWE_AUTH_SUCCESS` payload to a boolean indicating whether the signed message is valid and login/registration can continue.
NOTE: For now we will return from `siweAuthResponder` BEFORE login/registration... login/registration will come later at which point the payload for `SIWE_AUTH_SUCCESS` will look like `RegisterResponse | LogInResponse` or something.
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Depends on D6027