ipa-pki-retrieve-key: request AES encryption (with fallback)
    
    Update the ipa-pki-retrieve-key client to issue a request that
    specifies that AES encryption should be used.  If the server
    responds 404, fall back to a request *without* an algorithm
    parameter.  This handles both of the possible 404 scenarios:
    
    a) It is an old server that does not support extra Custodia key
       parameters;
    
    b) The server supports extra parameters but the key does not exist,
       in which case the fallback request will also fail with 404.
    
    Fixes: https://pagure.io/freeipa/issue/8020
    Reviewed-By: Alexander Bokovoy <abbra@users.noreply.github.com>