PostgreSQL 17 Beta 1 release announcement draft

Hi,

Attached is a copy of the PostgreSQL 17 Beta 1 release announcement
draft. This contains a user-facing summary of some of the features that
will be available in the Beta, as well as a call to test. I've made an
effort to group them logically around the different workflows they affect.

A few notes:

* The section with the features is not 80-char delimited. I will do that
before the final copy

* There is an explicit callout that we've added in the SQL/JSON features
that were previously reverted in PG15. I want to ensure we're
transparent about that, but also use it as a hook to get people testing.

When reviewing:

* Please check for correctness of feature descriptions, keeping in mind
this is targeted for a general audience

* Please indicate if you believe there's a notable omission, or if we
should omit any of these callouts

* Please indicate if a description is confusing - I'm happy to rewrite
to ensure it's clearer.

Please provide feedback no later than Wed 2024-05-22 18:00 UTC. As the
beta release takes some extra effort, I want to ensure all changes are
in with time to spare before release day.

Thanks,

Jonathan