[CT-423] Add missing index (#1039) (#1041)

* [CT-423] Add missing index

Fetching SELECT * FROM perpetual_positions WHERE "subaccountId" = subaccount_uuid AND "perpetualId" = perpetual_id ORDER BY "openEventId" DESC LIMIT 1 was very slow on mainnet.

indexer/packages/postgres/src/db/migrations/migration_files/20240202084811_add_perpetual_positions_open_event_id_index.ts

@@ -0,0 +1,18 @@
+import * as Knex from 'knex';
+
+export async function up(knex: Knex): Promise<void> {
+  // eslint-disable-next-line @typescript-eslint/quotes
+  await knex.raw(`
+    CREATE INDEX CONCURRENTLY IF NOT EXISTS "perpetual_positions_subaccountId_perpetualId_openEventId_index" ON "perpetual_positions" ("subaccountId", "perpetualId", "openEventId" DESC);
+  `);
+}
+
+export async function down(knex: Knex): Promise<void> {
+  await knex.raw(`
+    DROP INDEX CONCURRENTLY IF EXISTS "perpetual_positions_subaccountId_perpetualId_openEventId_index";
+  `);
+}
+
+export const config = {
+  transaction: false,
+};