fix: should support fieldsets in an `s-form`

[wesleyboar]

Overview

Allow s-form fields (<div>s) to be nested in a fieldset.

• So fieldsets can be used on s-form.
• So tapis-project/authenticator can easily disable fieds by disabling a fieldset.

Related

• required by https://github.com/tapis-project/authenticator/issues/79
  • not required since 488a107

Changes

• added fieldset with fields to form demos
• deleted idea about opt-out nested feild wrappers
• changed field wrappers to not have bottom margin if they are last child
• added support for s-form field wrappers to be nested in fieldsets

Testing

1. Open form demos e.g.
   • http://localhost:3000/components/detail/s-form--portal
   • http://localhost:3000/components/detail/django-cms-forms
   • http://localhost:3000/components/detail/c-form--portal
2. Verify field wrappers (and their fields) inside a fieldset render as if not in a fieldset.

UI

c-form	django-cms-forms	s-form