Feat(medusa, user, core-flows): User creation with invites (#6413)

**What**
- add accept invite endpoint 

**Invite accept flow**
- authenticate using the auth endpoint to create and auth-user
- invoke accept endpoint with token and info to create user

integration-tests/plugins/helpers/create-admin-user.ts

@@ -0,0 +1,25 @@
+import { IAuthModuleService } from "@medusajs/types"
+import { ModuleRegistrationName } from "@medusajs/modules-sdk"
+import adminSeeder from "../../helpers/admin-seeder"
+import jwt from "jsonwebtoken"
+import { getContainer } from "../../environment-helpers/use-container"
+
+export const createAdminUser = async (dbConnection, adminHeaders) => {
+  await adminSeeder(dbConnection)
+  const appContainer = getContainer()!
+
+  const authModule: IAuthModuleService = appContainer.resolve(
+    ModuleRegistrationName.AUTH
+  )
+  const authUser = await authModule.create({
+    provider: "emailpass",
+    entity_id: "admin@medusa.js",
+    scope: "admin",
+    app_metadata: {
+      user_id: "admin_user",
+    },
+  })
+
+  const token = jwt.sign(authUser, "test")
+  adminHeaders.headers["authorization"] = `Bearer ${token}`
+}