Fix styling of "Enabled OAuth sign-in sources" checkboxes

📖 What does this MR do?

Related to #29126 (closed)

Fixes the styling of the "Enabled OAuth sign-in sources" checkboxes in "Admin" -> "Settings" -> "General" -> "Sign-in restrictions". I am not 100% sure why they were originally styled like this. My theory is that we were originally using Bootstrap toggle buttons but these broke at somepoint when the JavaScript responsible for making these work was changed.

💻 Local testing

1. Modify gitlab.yml to add available omniauth providers. Find the development -> omniauth -> providers section and change to:

development:
  <<: *base
  omniauth:
    providers:
    - { name: 'google_oauth2',
        app_id: '',
        app_secret: '',
        args: { access_type: 'offline', approval_prompt: '' } }
    - { name: 'github',
        app_id: 'YOUR_APP_ID',
        app_secret: 'YOUR_APP_SECRET',
        url: "https://github.com/",
        verify_ssl: true,
        args: { scope: 'user:email' } }
    - { name: 'bitbucket',
        app_id: 'YOUR_APP_ID',
        app_secret: 'YOUR_APP_SECRET' }
    - { name: 'gitlab',
        app_id: 'YOUR_APP_ID',
        app_secret: 'YOUR_APP_SECRET',
        args: { scope: 'api' } }
    - { name: 'google_oauth2',
        app_id: 'YOUR_APP_ID',
        app_secret: 'YOUR_APP_SECRET',
        args: { access_type: 'offline', approval_prompt: '' } }
    - { name: 'facebook',
        app_id: 'YOUR_APP_ID',
        app_secret: 'YOUR_APP_SECRET' }
    - { name: 'twitter',
        app_id: 'YOUR_APP_ID',
        app_secret: 'YOUR_APP_SECRET' }

1. Restart GDK (gdk restart)
2. Navigate to "Admin" -> "Settings" -> "General" -> "Sign-in restrictions" and find the "Enabled OAuth sign-in sources" section (/admin/application_settings/general#js-signin-settings).

📷 Screenshots

Before	After

🚦 Does this MR meet the acceptance criteria?

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