feat(NcAppSidebar): add toggleAttrs prop to pass attributes on the toggle button

[ShGKme]

☑️ Resolves

• In Talk when we are in the call, we need the top bar to be dark-themed.
  In the past, we had a custom toggle button in the top bar with data-dark-theme on the top bar to archive that. Now with the built-in toggle button, it is not possible...
• Add toggleAttrs similar to toggleClasses prop to pass attributes on the toggle button
  • Allows to set data-them-dark manually from Talk
• Alternative:
  1. Add hideToggle prop to hide the default toggle button
  2. Add NcAppToggleButton to allow users to place it anywhere
  3. Connect this NcAppToggleButton with NcAppSidebar inside @nextcloud/vue
  4. Do not forget about slide animations for the custom toggle button

🖼️ Screenshots

🏚️ Before	🏡 After

🚧 Tasks

• Add toggleAttrs

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 3️⃣ Backport to next requested with a Vue 3 upgrade

[susnux]

Thank you!

[ShGKme]

/backport to next