Add a possibility of playing multiple difficulties of the same mapset in a multiplayer lobby

[adim2222]

Quick note before i begin: i haven't gotten that deep in the osu lazer code to know exactly how doable this is, but i still think it might be an awesome and easy to implement feature.

The multiplayer room in osu currently supports only one beatmap at the time, hovever i reckon it would be possible and sensible to add multi beatmap rooms.

For example there could be a multiplayer lobby setting to allow all difficulties of a map, and if selected by the host, all players have the ability to pick a difficulty of a map that suits them. This could be achieved by a simple dropdown menu on the player banner

This would provide more experienced players with a possibility of playing with complete begginers, and increase the compatibility of players in multi lobbies.

[Joehuu]

Already tracked in #5578.

[adim2222]

i searched for it i swear 😭