Permissions for the /avatar command

[tillpp]

Steps to Reproduce and Observed Behavior

i was thinking to have two types of entityModels
one that everyone can pick, like /avatar cubyz:snale and /avatar cubyz:cubert
and the other that can only be picked with admin rights, like /avatar cubyz:snail and /avatar cubyz:missing
and have a world specific file that defines which would be allowed for everyone

this is waiting for both the permission system with better parser ( #1425 ) and avatar system to be implemented (#2641 / #2652 ).

[Wunka]

If this is needed and we can't wait for #1425 then this can also be done without #1425 by just checking ourself if the user has permission. So something like this:

switch(arg) {
    inline else => |ent| source.hasPermission("/command/avatar/" ++ @tagName(ent));
}

[Wunka]

I did remember now. This needs the default permission group #2540 or atleast sometype of default permissions.