feat: Create flow model and graphQL mutation

packages/backend/src/models/flow.ts

@@ -0,0 +1,31 @@
+import Base from './base'
+import Step from './step'
+
+class Flow extends Base {
+  id!: number
+  userId!: number
+
+  static tableName = 'flows';
+
+  static jsonSchema = {
+    type: 'object',
+
+    properties: {
+      id: { type: 'integer' },
+      userId: { type: 'integer' }
+    }
+  }
+
+  static relationMappings = () => ({
+    steps: {
+      relation: Base.HasManyRelation,
+      modelClass: Step,
+      join: {
+        from: 'flows.id',
+        to: 'steps.flow_id',
+      },
+    }
+  })
+}
+
+export default Flow;