FINERACT-2759: Add issuance and expiry dates to client identifiers

[AnvayKharb]

Description

Adds optional issuance and expiry dates to client identifiers.

This change:

• Adds issuance_date and expiry_date to m_client_identifier
• Exposes issuanceDate and expiryDate through create, retrieve, and update APIs
• Supports clearing the dates using explicit null
• Updates API documentation and Swagger models
• Adds integration coverage for create, retrieve, update, and optional date behavior

Existing client identifiers remain backward compatible.

Related Issue

FINERACT-2759

[IOhacker]

LGTM