QueryForDeferredCredential to support, if possible automatic refresh of access_token

[babisRoutis]

The interface QueryForDeferredCredential expresses the ability of the library (and the wallet) to query the deferred endpoint of a credential issuer, in order to get the actual credential.

Given that

• access to the deferred endpoint require an access_token
• deferred endpoint could be queried after the actual issuance

There should be a way, to refresh the access_token (bearer or DPoP), if the authorization server had provided a refresh_token

Unfortunately, it is not clear how to obtain an access_token when either

• the refresh_token has expired or
• the server didn't provide a refresh_token