Defaulting to password_encryption = scram-sha-256

Hi,

Now that we probably have shaken the worst issues out of scram,
shouldn't we change the default password_encryption to something that
doesn't scare people?   The only reason I could think of not wanting to
do that for is that we don't necessarily guarantee that we have a strong
random generator, but if that's the issue, we should change initdb to
default it to something safe if the platform provides something. Which
is just about any sane one, no?

Greetings,

Andres Freund