feat: Create execution step model

packages/backend/src/db/migrations/20220219100800_create_execution_steps.ts

@@ -0,0 +1,18 @@
+import { Knex } from 'knex';
+
+export async function up(knex: Knex): Promise<void> {
+  return knex.schema.createTable('execution_steps', (table) => {
+    table.increments('id');
+    table.integer('execution_id').references('id').inTable('executions');
+    table.integer('step_id').references('id').inTable('steps');
+    table.string('status');
+    table.text('data_in');
+    table.text('data_out');
+
+    table.timestamps(true, true);
+  });
+}
+
+export async function down(knex: Knex): Promise<void> {
+  return knex.schema.dropTable('execution_steps');
+}