Update Introduction to only support authenticated users

[derekhouck]

Description

Per discussion with Matt on 10/4: Forms created by this tool should require authentication by default. Support for unauthenticated forms may be a future feature, but we do not need to worry about it now.

In other words, we don't want a link on the Introduction page of any forms we render that allows a Veteran to continue to the form without signing in.

Update: The zero-silent-failures initiative makes it almost certain that we will always require login going forward. We can't notify people of failures if we don't know who they are.

Acceptance Criteria:

• [ ] Link to continue to form without authenticating is not present on the Introduction page of forms rendered by the form-renderer app.

[derekhouck]

See VA Form 526 for possible example authentication-required form.

[Karak888]

can't proceed past introduction page as it is now- so this is necessary task. Form 526 potential authenticated experience for Derek to reference.