- Add storing bot response messages in postgres

- Add scheduled task to clean up said store

PluralKit.Core/Database/Database.cs

@@ -19,7 +19,7 @@ namespace PluralKit.Core
     internal class Database: IDatabase
     {
         private const string RootPath = "PluralKit.Core.Database"; // "resource path" root for SQL files
-        private const int TargetSchemaVersion = 10;
+        private const int TargetSchemaVersion = 11;
         
         private readonly CoreConfig _config;
         private readonly ILogger _logger;

PluralKit.Core/Database/Migrations/11.sql

@@ -0,0 +1,17 @@
+-- SCHEMA VERSION 11: (insert date) --
+-- Create command message table --
+
+create table command_message
+(
+	message_id bigint primary key,
+	invoker_id bigint not null,
+	timestamp timestamp not null default now()
+);
+
+create function cleanup_command_message() returns void as $$
+begin
+    delete from command_message where timestamp < now() - interval '1 minute';
+end;
+$$ language plpgsql;
+
+update info set schema_version = 11;

PluralKit.Core/Database/Repository/ModelRepository.CommandMessage.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+using System.Data;
+using System.Threading.Tasks;
+
+using Dapper;
+
+namespace PluralKit.Core
+{
+    public partial class ModelRepository
+	{
+		public Task SaveCommandMessage(IPKConnection conn, ulong message_id, ulong author_id) =>
+			conn.QueryAsync("insert into command_message (message_id, invoker_id) values (@Message, @Author)",
+				new {Message = message_id, Author = author_id });
+	}
+}