playlist scroll pos

[mono424]

Motivation and Context

If the playlist sidebar is not visible on page start, the scroll position is not set to the active item.

https://github.com/TUM-Dev/gocast/assets/17506411/ab908c9c-60e0-4656-8336-c8e4f9803a56

Description

This pr adds a observer that scrolls to the right position upon sidebar open.

Steps for Testing

Prerequisites:

• 1 Students

1. Log in
2. Navigate to a Livestream
3. Check if its scrolled to the right item if you open the playlist sidebar

Screenshots

https://github.com/TUM-Dev/gocast/assets/17506411/f96f7a1a-ed2c-472e-a974-6197e7dd8f89

[github-actions[bot]]

Your Testserver will be ready at https://1120.test.live.mm.rbg.tum.de in a few minutes.

Logins

| Kurs1 | Kurs2 | Kurs3 | Kurs4 | | ---------------------------------------- | ------------------------- | ------------------------- | ------------------------- | | public | public | loggedin | enrolled | | prof1 | prof1 | prof2 | prof1
prof2 | | student1
student2
student3 | student1
student2 | student2
student3 | student1
student2 |

[joschahenningsen]

What's the status of this? @mono424

[mono424]

What's the status of this? @mono424

Its ready to get reviewed :)