[OID4VCI] Restructure credential_configurations_supported parsing to handle credential_metadata with display and claims && Update Credential Issuer Metadata structure

[forkimenjeckayang]

Summary

Implements complete OID4VCI draft-16 specification changes for Credential Issuer Metadata, including restructured credential_configurations_supported with credential_metadata and new credential_request_encryption support.

Key Changes

• New CredentialMetadata class: Container for display and claims metadata
• Updated SupportedCredentialConfiguration: Removed direct display and claims fields, added credential_metadata field
• Enhanced DisplayObject: Added support for background_image and enhanced logo object structure
• New CredentialRequestEncryptionMetadata: Supports credential request encryption with JWKS, algorithms, and compression
• Enhanced CredentialResponseEncryptionMetadata: Added zip_values_supported field
• Updated CredentialIssuer: Added credential_request_encryption field
• Updated tests: All integration tests updated to use new structure and validate new fields

Breaking Changes

• SupportedCredentialConfiguration.getDisplay() and getClaims() methods removed
• New API: getCredentialMetadata().getDisplay() and getCredentialMetadata().getClaims()
• Null checks required when accessing credential_metadata

Specification Compliance

• Follows OID4VCI draft-16 structure completely
• Prioritizes format-specific metadata over fallback metadata
• Supports all required and optional fields for both request and response encryption
• Implements proper credential metadata structure with display and claims

Closses

• Ticket: Keycloak: Restructure credential_configurations_supported parsing to handle credential_metadata with display and claims #76
• Ticket: Keycloak: Clean up and update the Credential Issuer Metadata model #78

[Ogenbertrand]

I did most of the work on this PR: #103 that contains credential_request_encryption and credential_response_encryption see tickets awell:
#74
#75

Perhaps you could refer my PR link for clarification, let's avoid double work.
WDYT @forkimenjeckayang @IngridPuppet ?

Aside that, this PR LDTM !

[IngridPuppet]

Added some comments. Please could you check?

[IngridPuppet]

I did most of the work on this PR: #103 that contains credential_request_encryption and credential_response_encryption see tickets awell: #74 #75

Perhaps you could refer my PR link for clarification, let's avoid double work. WDYT @forkimenjeckayang @IngridPuppet ?

Aside that, this PR LDTM !

I'm afraid the double work, if any, is already done. Given the significant progress on this PR, you could just indeed sync on overlapping changes so it is straightforward to resolve conflicts to arise in the future.