Keycloak: Update credential response (even if deferred) to always return an array when not returning a transaction_id

### Description

Changelog
>    * credential response always returns an array when not returning a transaction_id with the option for additional meta-data
>    * deferred credential response always returns an array (same as credential response)

https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0-15.html#name-credential-response