ssi-jwk: Derive macro

[timothee-haudebourg]

Add a derive macro to automatically implement the JwsPayload, ValidateJwsHeaders and JwtClaimSet for custom JWT types.

For example:

#[derive(Clone, Jwt)]
#[jwt(typ = "oauth-client-attestation+jwt")]
pub struct ClientAttestation {
    pub iss: Issuer,
    pub sub: Subject,
    pub exp: ExpirationTime,
    pub cnf: Confirmation,
    pub iat: Option<IssuedAt>,
    pub nbf: Option<NotBefore>,

    #[serde(flatten)]
    pub other: AnyClaims,
}