[Audio] Update default forced application.yml

[aikaterna]

What Red version are you using?

3.5.10

What were you trying to do?

Play yt videos.

What did you expect to happen?

Effortless playback.

What actually happened?

A 403 error because we don't have the youtube-source plugin configured correctly.

How can we reproduce this error?

1. Be on an affected machine/vps
2. Play a yt video.
3. Experience a 403 error because we should be trying other sources on the plugin first, before the ones defined in the base default configuration.
   ...

Anything else?

We should be using an application.yml that's structured in this manner instead of what we are currently distributing: Cog-Creators/Lavalink-Jars#15 (comment)
We need to consider the changes made in #6373 - we need to test whether the plugin fails when not configured properly: "As for the configuration, it depends on what happens when the plugin isn't on the list of plugins (as is the case when you disable yt source in settings). If it means that LL won't start then that place will not be suitable. This is how we do things for the plugin now, it's not always present" (referring to #6373)
The changes should be made in the area starting at this line:

Red-DiscordBot/redbot/cogs/audio/utils.py

Line 57 in fa7236a

DEFAULT_LAVALINK_YAML = {