Feature parity mismatch between add_command and queue_command functions

[kshannoninnes]

Currently add_command/4 has a handle_call overload that handles lists of guild_ids. queue_command/3 does not have this. Related to the recent issue, if we go the route of updating the docs to reflect the correct use of the list overload, should an equivalent overload be added for process_queued_commands as well? If not, I think we should remove the list overload for add_command/4.

In either case, I think docs could be updated to better reflect how a user could register commands to multiple guilds, even if it's just an example using the Enum module. Having explicit instruction for this can help avoid issues such as users trying to pass a list to add_command4/queue_command/3

[kshannoninnes]

Personally I think we should leave registering commands to multiple guilds up to the users. It allows for more fine-grained control over error handling (eg. logging/retrying/etc). Looking for other opinions though.