feat(webhooks): init, add service/models, add JSON to patch objects

PluralKit.Core/Database/Migrations/20.sql

@@ -0,0 +1,7 @@
+-- schema version 20: insert date
+-- add outgoing webhook to systems
+
+alter table systems add column webhook_url text;
+alter table systems add column webhook_token text;
+
+update info set schema_version = 20;