Opt out of guild creates at startup

[muddyfish]

When connecting to a shard, you receive a full list of guild create events. When you're on large bot scaling, that's a very large amount of bandwidth.

Sometimes you know in advance that you either won't need any guild creates, or otherwise a filter for ones you know you aren't caching currently.

I'd implement this by adding a guild_denylist attribute to the identify payload, and ignoring those guilds when sending the initial wave of creates. (A denylist rather than allowlist means you can keep receiving new guilds you hadn't joined before.)

I estimate that with this change, I'd be able to startup 4-5 times faster, as I'm network limited during startup.