Add a divider between tasks list and tasks details for tablets

Description

Adds a divider between tasks list and task details for tablets so as to separate both views and also so that floating action buttin doesn't look like its floating in middle.

Screenshots

The screenshots can be found here

Technical details

Tests

Issues

https://gitlab.e.foundation/e/os/backlog/-/issues/2678

10 commandments of code reviews

👪 ❤ https://gitlab.e.foundation/internal/wiki/-/wikis/mobile-team/guidelines/Code-review