Use offline mode for keylist with validation

We need to list keys in keylist mode validate to
get trust and trustchain information for X509
certificates. By default this includes CRL / OCSP
checks. The new "offline" mode introduced with
gpgsm 2.1.6 allows us to list all keys with validation
but without consulting remote sources.

This speeds up the time until Kleopatra is usable
as an application or as an UI Server drastically
as CRL checks can be infinitley slow and old keyrings
with a lot of certificates might also include a lot
of broken CRL servers that would be queried until
the fetch operation times out.

BUG: 339385
REVIEW: 124950