Change default value of `showBackButton` to `true` for `NavigationButtons`

[bjosttveit]

Description

We should consider changing the default value of showBackButton to true for the NavigationButtons component in an upcoming major version. It's a little strange that you manually have to set "showBackButton": true on every NavigationButtons component where you want the back button to show. It's only visible as long as there is something to navigate back to, so this should really only be set to false under very specific circumstances. This is especially true since the back arrow button was removed in #2831.

Additional Information

No response