feat: enhance session response

[bjoern-m]

Description

This PR introduces improvements to the session validation process, focusing on extracting claims from JWT tokens.

Implementation

• dto/session.go:

  • Added a new Claims struct to represent JWT claims, providing a standardized structure for parsing token data.
  • Implemented GetClaimsFromToken function for parsing and validating JWT token claims.
  • Updated ValidateSessionResponse to include the Claims field while keeping deprecated fields (ExpirationTime, UserID) for backward compatibility.

• handler/session.go:

  • Replaced manual token parsing with GetClaimsFromToken for extracting claims.
  • Simplified logic in ValidateSession and ValidateSessionFromBody handlers:
    • Validated session IDs and claims directly.
    • Updated response payload to use the new Claims structure.

Todos

• Deprecate usage of ExpirationTime and UserID in the SDK and migrate to the new structure.

Additional Context

This PR relates the the changes made in the docs: teamhanko/docs#110