Convert the sign-up settings section from Rails to Vue

What does this MR do?

Converts the form found in Admin Area > Settings > General > Sign-up Restrictions from a Ruby on Rails based form to a Vue controlled form.

This is the first step required for having a stateful confirmation modal as described in #293018 (closed)

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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Security

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