Support multiple matching keys (id, cio_id) in Customer.io destination

### Connector Name

customer io

### Connector Version

0.3.19

### What step the error happened?

None

### Relevant information

The current Airbyte Customer.io destination connector only supports person_email as a matching key for person_identify.

However, Customer.io natively supports multiple identifiers (id, cio_id, email), and many production systems rely on ID-based identity rather than email.

This limitation causes incorrect identity resolution and duplicate user creation.

### Relevant log output

```shell

```

### Contribute

- [ ] Yes, I want to contribute

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**Internal Tracking:** https://github.com/airbytehq/oncall/issues/11715