Fixes#24447
This factory type, which is really more a data holder/connection producer
per connection instance, creates, if using https, a new certificate_credentials
on every instance. Which when used by S3 client is per client and
scheduling groups.
Which eventually means that we will do a set_system_trust + "cold" handshake
for every tls connection created this way.
This will cause both IO and cold/expensive certificate checking -> possible
stalls/wasted CPU. Since the credentials object in question is literally a
"just trust system", it could very well be shared across the shard.
This PR adds a thread local static cached credentials object and uses this
instead. Could consider moving this to seastar, but maybe this is too much.
Closesscylladb/scylladb#24448
(cherry picked from commit 80feb8b676)
Closesscylladb/scylladb#24461
