chore: move migrations to rust

also adds some basic test seed data

PluralKit.Core/Database/Migrations/7.sql

@@ -1,35 +0,0 @@
--- SCHEMA VERSION 7: 2020-06-12
--- (in-db message count row)
-
--- Add message count row to members table, initialize it with the correct data
-alter table members add column message_count int not null default 0;
-
-update members set message_count = counts.count
-from (select member, count(*) as count from messages group by messages.member) as counts
-where counts.member = members.id;
-
--- Create a trigger function to increment the message count on inserting to the messages table
-create function trg_msgcount_increment() returns trigger as $$
-begin
-    update members set message_count = message_count + 1 where id = NEW.member;
-    return NEW;
-end;
-$$ language plpgsql;
-
-create trigger increment_member_message_count before insert on messages for each row execute procedure trg_msgcount_increment();
-
-
--- Create a trigger function to decrement the message count on deleting from the messages table
-create function trg_msgcount_decrement() returns trigger as $$
-begin
-    -- Don't decrement if count <= zero (shouldn't happen, but we don't want negative message counts)
-    update members set message_count = message_count - 1 where id = OLD.member and message_count > 0;
-    return OLD;
-end;
-$$ language plpgsql;
-
-create trigger decrement_member_message_count before delete on messages for each row execute procedure trg_msgcount_decrement();
-
-
--- (update schema ver)
-update info set schema_version = 7;