PHP 8.1 transition plan

[Bryce Harrington]

Hi devs,

I've started on the php 8.1 transition, details are here:

  https://wiki.ubuntu.com/ServerTeam/Transition/Php8.1
  https://people.canonical.com/~ubuntu-archive/transitions/html/html/php8.1.html

I anticipate this PHP update will be straightforward; the challenge will
be getting it completed prior to the OpenSSL 3.0 transition starting, as
the two certainly have potential for intertwining.  The OpenSSL
transition starts the week of Nov 4th, so that gives 2 weeks, which is a
bit tight for transitioning php but potentially doable if no major
troubles crop up.

The php8.1 language runtime itself has been uploaded to -proposed for
universe; it won't migrate to release until the full transition is
complete.  php8.0 will remain in the archive until that point.

I've updated php-defaults in -proposed to set 8.1 as the default.  This
allows no-change rebuilds of various php components to build against
that version.  This rebuilding of the PHP ecosystem is what consumes
most of the time for this transition, and of course help's always
welcome.

Bryce