configure: Bump sonames

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
NEWS: Write entry for 6.0

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
po: add pulseaudio.service.in to POTFILES.in

Signed-off-by: David Henningsson <david.henningsson@canonical.com>