feat(bot): add Redis cache

PluralKit.Bot/Init.cs

@@ -2,6 +2,7 @@ using Autofac;
 
 using Microsoft.Extensions.Configuration;
 
+using Myriad.Cache;
 using Myriad.Gateway;
 using Myriad.Types;
 using Myriad.Rest;
@@ -51,6 +52,10 @@ public class Init
             if (config.UseRedisRatelimiter)
                 await redis.InitAsync(coreConfig);
 
+            var cache = services.Resolve<IDiscordCache>();
+            if (cache is RedisDiscordCache)
+                await (cache as RedisDiscordCache).InitAsync(coreConfig.RedisAddr, config.ClientId!.Value);
+
             if (config.Cluster == null)
             {
                 // "Connect to the database" (ie. set off database migrations and ensure state)