[web] Convert models and self-referential test files to ESM (#29521)

from overleaf/ar-models-es-conversion

GitOrigin-RevId: a92ab8342c0f3e23155eacc0570458fc910c3d71

services/web/app/src/models/UserFeatureUsage.mjs

@@ -0,0 +1,19 @@
+import mongoose from '../infrastructure/Mongoose.js'
+const { Schema } = mongoose
+
+const Usage = new Schema({
+  usage: { type: Number },
+  periodStart: { type: Date },
+})
+
+export const UserFeatureUsageSchema = new Schema({
+  features: {
+    aiErrorAssistant: Usage,
+    aiWorkbench: Usage,
+  },
+})
+
+export const UserFeatureUsage = mongoose.model(
+  'UserFeatureUsage',
+  UserFeatureUsageSchema
+)