[ixpmanager] Upgrade from 4x to 6x

[Barry O'Donovan (INEX)]

Hi Kyle,

hope you're well. Glad it all went well.

Some inline comments below for mailing list archival purposes for anyone 
coming upon this.

  - Barry

Kyle Spencer wrote on 08/04/2022 02:40:
> 1) There were a couple cases where "php composer.phar update" needed
> to be run before the "php composer.phar install" command would work
> successfully.

This is one of the issues falling behind on upgrades - older releases 
would have been 'composed' against older versions of PHP. Doing the 
update as above is the right way to try and get past this issue.

> 2) The PHP PPA now pulls in 8.1 packages and the documentation/scripts
> reference 8.0. We are now running on 8.1 and the documentation/scripts
> might benefit from being updated to reflect this.

Current release of IXP Manager is supported for PHP versions >8.0 (which 
is to say 8.0 and 8.1) so no issue here.