Re: recovery modules

Here is a new revision of the restore modules patch set.  In this patch
set, the interface looks similar to the recent archive modules redesign,
and there are separate callbacks for retrieving different types of files.
I've attempted to address all the feedback I've received, but there was a
lot scattered across different threads, so it's possible I've missed
something.  Note that 0001 is the stopgap fix for restore_command that's
being tracked elsewhere [0].  I was careful to avoid repeating the recent
mistake with the SIGTERM handling.

This patch set is still a little rough around the edges, but I wanted to
post it in case folks had general thoughts about the structure, interface,
etc.  This implementation restores files synchronously one-by-one just like
archive modules, but in the future, I would like to add
asynchronous/parallel/batching support.  My intent is for this work to move
us closer to that.

[0] https://postgr.es/m/20230214174755.GA1348509%40nathanxps13

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com