Backport #27723 by @mpldr
This patchset changes the connection string builder to use net.URL and
the host/port parser to use the stdlib function for splitting host from
port. It also adds a footnote about a potentially required portnumber
for postgres UNIX sockets.
Fixes: #24552
Co-authored-by: Moritz Poldrack <33086936+mpldr@users.noreply.github.com>
