Store stard status in the database

PluralKit.Core/Database/Migrations/14.sql

@@ -0,0 +1,15 @@
+-- SCHEMA VERSION 14: 2021-06-10 --
+-- Add shard status table --
+
+create table shards (
+    id int not null primary key,
+    
+    -- 0 = down, 1 = up
+    status smallint not null default 0,
+    
+    ping float,
+    last_heartbeat timestamptz,
+    last_connection timestamptz
+);
+
+update info set schema_version = 14;