[FEATURE] Introduce Pluggable Identity Provider (IdP) Interface for Email Authentication

[Aravinda-HWK]

Summary

Description

The email system currently works with only one Identity Provider.
This IdP is tightly coupled to the system.

We need to introduce a pluggable IdP interface so that any IdP can be connected without changing the core email code.

The email system should use a common interface for authentication and user lookup, and each IdP should be implemented as a separate module.

Why is this feature needed?

• The email system is not tied to a single IdP
• New IdPs can be added easily
• Existing idp integration works through the new interface

Alternatives Considered

No response

Additional Context

Acceptance Criteria

• A common IdP interface is defined
• Existing idp uses this interface
• IdP can be selected using the configuration

[Aravinda-HWK]

Close this issue because the architecture of the system was changed.