[Feature Request]: Bookmark Exisiting Playlists

### Guidelines

- [x] I have searched the issue tracker for [open](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aopen+is%3Aissue) and [closed](https://github.com/FreeTubeApp/FreeTube/issues?q=is%3Aissue+is%3Aclosed) issues that are similar to the feature request I want to file, without success.
- [x] I have searched the [documentation](https://docs.freetubeapp.io/) for information that matches the description of the feature request I want to file, without success.
- [x] This issue contains only one feature request.

### Problem Description

Channels have existing playlists that may continue to have videos added to them upon release by their content creators.

In order to save/bookmark the playlist to come back to easily I have to recreate the playlist and add the videos manually to the playlist that I created locally. If new videos were to be added to the original channel playlist from the content creator then I must periodically return to the channel, check for a new video, and manually add it to my custom playlist.

### Proposed Solution

Let people save an existing channel playlist to our playlist tab and then have it update with new videos as the content creator adds them

### Alternatives Considered

Display a notification and/or badge counter that a new video was added

### Issue Labels

ease of use improvement

### Additional Information

Example: MangoJelly Solutions for FreeCAD channel has a playlist called "[Basic Beginners FreeCAD v1 (Public)](https://youtube.com/playlist?list=PLWuyJLVUNtc3UYXXfSglVpfWdX31F-e5S)".

I am learning how to use the software so I wanted to save the playlist so I can easily access it to practice the next lesson.

I had to create a new playlist for myself, name it the same thing, and manually add each video to it and add the playlist's description as well. At the time I created it the content creator had 24 lessons in the original. I recently checked back on his original playlist and found that I was not aware of lesson 25 that released 5 days prior, I then manually added lesson 25 to my personal recreation of said playlist.