Add Sepia PeerTube instances to settings view

[mblomdahl]

When viewing the app settings— apart from selecting from the existing pre-defined backends —we should offer the user to add any other instance from Sepia. A button with text "Add from Sepia instances' list" which opens a select element with instances.

Hosts lists come from https://instances.joinpeertube.org/api/v1/instances?start=0&count=1000&sort=-createdAt and could be rendered like so:

• wrtube.wrservices.lat – WR Services Media (20)
• tankie.tube – TankieTube (2)
• videos.globenet.org – Vidéos Globenet (42)
• videomensoif.ynh.fr – Mensoif Tube (423)
• ...

The number within the parenthesis is the "totalLocalVideos" count for each site, and sites which have 0 local videos they should not be listed/selectable.

Update 2024-07-03: About improving the capabilities of the Sepia API, created https://framagit.org/framasoft/peertube/instances-peertube/-/issues/50

[mykhailodanilenko]

Closed by #96