[ui-react] it should be easy to add custom fields in SignUp form in hosted UI

[dfang]

Is your feature request related to a problem? Please describe.
I'm always frustrated when i want to add a simple custom field (role with select or radio button) to sign up field with HOSTED REACT UI.

Describe the solution you'd like
easy to add any custom field type to sign up or sign in form

Describe alternatives you've considered
i try to extend AmplifySignout in my custom_signup.jsx, but i got this error

class CustomSignUp extends AmplifySignUp 

TypeError: Class extends value #<Object> is not a constructor or null

Additional context
Add any other context, an idea of the implementation or screenshots about the feature request here.

<AmplifyAuthenticator>
          <CustomSignUp />
          <AmplifySignUp
            slot="sign-up"
            usernameAlias="email"
            formFields={[
              // { type: "username" },
              { type: "email" },
              { type: "password" },
              {
                type: "custom:role",
                label: "Custom Role Label",
                key: "custom:role",
                placeholder: "custom Phone placeholder",
                required: false,
              }
            ]}
          />
        </AmplifyAuthenticator>

it's easy to add custom field to Sign Up Form, but that field can only be input, but what if i want a select or a radio button group ? it seems it can't be customized,

[tomyitav]

+1, having a select on the SignUp page will be very helpful

[hkjpotato]

related https:/aws-amplify/amplify-js/issues/7937. Feature request for supporting customized form field (other than Input)

[ericclemmons]

I just documented an example that specifically adds a custom field (preferred_username) for our @next release (see #552):

https://ui.docs.amplify.aws/ui/components/authenticator?platform=react#sign-up-fields

To be clear, this is for customizing the Authenticator's sign-up field – not Cognito Hosted UI. (That's not possible via this library and can only be done by the Cognito service team)