[mock][store] Storing an object that its id is different with the key

I want to store a customer by its token. This is a sample code:

```ts
store.set('Customer', token, customer);
```

But I get this error:

Field id is a key field of Customer and you are trying to set it to `` while the key is ``

It would be great if I can store objects with any arbitrary key.

**Why do we need this feature?**
Using a token as a key, we can have multiple versions of any mocked customer. Then the mock server will be able to handle multiple e2e tests that are running for the same `customerId` in different sessions.

No file or test is named. Start by locating the mock store implementation and the validation that rejects a key differing from the object's id, using the `store.set('Customer', token, customer)` example and reported error as entry points. Done means arbitrary keys can store multiple mocked customer versions for separate sessions.

Written by the indexing model from the issue text.