Improve PHP 8.1 support with Installer

[browniebraun]

Describe the bug

Clean installation of 1.2.x branch, version 1.2.23, shows deprecated messages directly when the install wizard starts.

Action failed
Sorry, we could not process your last action.
Error:	200 OK
Reason:	
Deprecated: escapeshellcmd(): Passing null to parameter #1 ($command) of type string is deprecated in /var/www/html/cacti/lib/functions.php on line 4473

Deprecated: file_exists(): Passing null to parameter #1 ($filename) of type string is deprecated in /var/www/html/cacti/lib/installer.php on line 791
{"Mode":1,"Step":1,"Errors":[],"Eula":null,"Prev":{"Text":"Previous","Step":0,"Enabled":false,"Visible":true},"Next":{"Text":"Begin","Step":2,"Enabled":false,"Visible":true},"Test":{"Text":"Test Connection","Step":-4,"Enabled":true,"Visible":false},"Theme":"midwinter","StepData":{"Eula":null,"Theme":"midwinter","Language":"en-US"},"Html":"

Screenshots

Desktop (please complete the following information)

• OS: [e.g. iOS]

Ubuntu 22.04.1 LTS

[browniebraun]

More output generated within final step of the installation wizard:

Deprecated: Implicit conversion from float-string "1670175096.0354" to int loses precision in /var/www/html/cacti/lib/installer.php on line 2654 {"Mode":null,"Step":"97","Errors":[],"Eula":"1","Prev":{"Text":"Previous","Step":96,"Enabled":true,"Visible":false},"Next":{"Text":"Next","Step":98,"Enabled":true,"Visible":false},"Test":{"Text":"Test Connection","Step":-4,"Enabled":true,"Visible":false},"Theme":"midwinter","StepData":{"Current":"41","Total":100},"Html":"

[TheWitness]

Working.

[TheWitness]

Should be good now.