Add schema changes for autoproxy

PluralKit.Core/Migrations/3.sql

@@ -0,0 +1,13 @@
+-- Same sort of psuedo-enum due to Dapper limitations. See 2.sql.
+-- 1 = autoproxy off
+-- 2 = front mode (first fronter)
+-- 3 = latch mode (last proxyer)
+-- 4 = member mode (specific member)
+alter table system_guild add column autoproxy_mode int check (autoproxy_mode in (1, 2, 3, 4)) not null default 1;
+
+-- for member mode
+alter table system_guild add column autoproxy_member nullable references members (id) on delete set null;
+
+-- for latch mode
+-- not *really* nullable, null just means old (pre-schema-change) data.
+alter table messages add column guild bigint nullable default null;