Add support for exp and iat on Request Object

[zandbelt]

Discussed in #1136

^{Originally posted by pasqualebarbaromind November 23, 2023}
The OIDCRequestObject config doesn't provide any option to add the exp (expiration) and iat (issued at) claims.
Since these claims in request object are adopted by some specifications such as https://openid.net/specs/openid-federation-1_0.html#name-using-a-request-object it would be great to have them added in the OIDCRequestObject configuration.