[CMS-449] Graceful version handling (#2267)
[CMS-449] Graceful version handling (#2267)

* Print message and exit for PHP <7.0 or >=8.1

* Encourage updating PHP, soft 8.1 incompatibility msg

* Semi-firm PHP 8.1+ support fail
pantheon-systems/cli,pantheon-systems/cli,pantheon-systems/cli