[Feature Request] Auto shuffle for URL-based playlist

**Is your feature request related to a problem? Please describe.**
In my channel, there aren't predefined file-based playlist. People have favorites youtube playlists URL's and they always have to manually shuffle playlist after each time they put play command.

**Describe the solution you'd like**
guild-level configuration something like always_shuffle

**Describe the basic flow/steps of using this feature**
How this feature would be used:
1. Set always_shuffle = true in serversettings.json
2. Enjoy the time saved from typing 'shuffle' command :)

**Additional context**
Title says 'URL-based playlist' just to clarify that I do not use file based playlists. However, I think for consistense sake such property like always_shuffle could work as default for all types of playlists.

**Have you confirmed that this idea is not already described here?**
https://github.com/jagrosh/MusicBot/projects/1
Yes

Start by locating the serversettings.json configuration handling and the playlist playback flow. Determine where an always_shuffle setting would apply to URL-based and other playlists, then verify that enabled servers automatically shuffle without requiring the shuffle command.

Written by the indexing model from the issue text.