[Feature Request]: Add Shuffle button within both YouTube and User 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

In the 'Playlists' feature. I can click on a playlist and sort by many different options.
#1. I clicked on 'Custom' in the sort by clause. I don't know what this is sorting by.
#2. I'd LIKE to sort by RANDOM (so that every time I listen to this playlist, it is in a new order).

### Proposed Solution

I'd like to be able to 'Sort By: Random'
I have 103 songs in this playlist. I think that 10 songs are the same SONG but different ReMixes.
I want to keep all the 'Duplicates' but I want to listen to them. I just don't want to sort alphabetically, because then I have 12 copies of the song 'IDGAF' (by Dua Lipa).

Again, I WANT to listen to all of these mixes. I just don't want to listen to them ONE RIGHT AFTER THE OTHER.

### Alternatives Considered

As an alternative, if you could just explain what the 'Sort Order: Custom' does. This MIGHT already do what I want (but I think that it merely allows me to do a CUSTOM re-ordering of the songs (doing drag and drop).


### Issue Labels

ease of use improvement

### Additional Information

I started by taking a copy of THIS playlist.
https://www.youtube.com/playlist?list=PLfqxLOyMxF2-c6P8d185EM4HcjgrYzAEl
I clicked each song in the list to add it to my 'Default Playlist'. That generally works.

I just ALSO wish that there was an easier way to import a BUNCH of playlists to SQLITE.
My PRIMARY FEATURE is to be able to access these playlists via SQLITE. I assume that I can do that (once I copy the playlist into FreeTube)?

I'll go test that feature soon. I'm beginning to use SQLITE for EVERYTHING!

Start by reviewing the playlist sorting controls and the linked pull request #6153. Confirm how Custom sorting currently works, then define completion as a shuffle option that produces a new order in both YouTube and user playlists without removing duplicates.

Written by the indexing model from the issue text.