Email-based user lookup and jobTitle standardization

Added an optional email filter to GET /iam/v1/users for direct, stable user lookup by email.

Extended POST /iam/v1/users/invite to accept firstName, lastName, and jobTitle.

Standardized the user schema on jobTitle across list, update, and invite APIs, deprecating jobFunction.

For backward compatibility, the API still accepts jobFunction in requests. If a client sends jobFunction instead of jobTitle, the server automatically copies the value into jobTitle and processes it as if jobTitle had been sent. However, we recommend updating your calls to use jobTitle.