Feature request: Add support for upserting HubSpot contact records by unique custom identifier instead of email

[lukewatters-airbyte]

Currently, the HubSpot destination only supports email as the unique identifier for contact record upserts. This limitation impacts workflows where a significant portion of contacts (e.g., 75%) do not have email addresses. HubSpot's API supports using a unique custom identifier for upserts, as detailed in their API documentation: https://developers.hubspot.com/docs/api-reference/crm-contacts-v3/guide. Adding this feature would greatly enhance the usability of Airbyte's HubSpot data activation for such use cases.