feat(#13): add calendar subscriptions migration

src/GmRelay.Bot/Migrations/V011__add_calendar_subscriptions.sql

@@ -0,0 +1,11 @@
+CREATE TABLE calendar_subscriptions (
+    id                  UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    token               TEXT UNIQUE NOT NULL,
+    user_telegram_id    BIGINT NOT NULL,
+    group_id            UUID REFERENCES game_groups(id) ON DELETE CASCADE,
+    filter_type         SMALLINT NOT NULL DEFAULT 0,
+    created_at          TIMESTAMPTZ NOT NULL DEFAULT now(),
+    expires_at          TIMESTAMPTZ
+);
+
+CREATE INDEX ix_calendar_subscriptions_user_telegram_id ON calendar_subscriptions (user_telegram_id);