Efflux: Avoid generating error logs by installer.pl

[eyazi]

Proposed change

The installer.pl generates numerous error messages during the installation of Znuny – even if everything works fine. This PR tries to eliminate some/most of them.

Type of change

• '1 - 🐞 bug 🐞' - Bugfix (non-breaking change which fixes an issue)

Additional information

Kernel/Modules/Installer.pm: PrintError makes sure failed database calls don't get handled by Perl (→ the web server). Every major error will either get directly shown to the user via $DBI::errstr or there is an existing translation message attached to it. Just by checking that the database is empty (by checking if the valid table exists), an error message gets created. Most of the other checks will also get logged as errors.

Kernel/System/Package.pm: var/packages will most likely not exist on > 95% of the installed systems. The subroutine does currently not check if the directory exists and throws an error.

Kernel/Output/HTML/Layout.pm: Both subroutines that got wrapped into the InstallerOnly check, make direct calls to the database, which does not exist yet (or at least shouldn't). InstallerOnly doesn't get used anywhere else, but it feels like this is a perfect use for it.

I don't think internal checks should write error messages to the log. This might give the wrong (first) impression that something went wrong or could have been done better.

Checklist

• The code change is tested and works locally.(❗)
• There is no commented out code in this PR.(❕)
• You improved or added new unit tests.(❕)
• Local ZnunyCodePolicy passed.(❕)
• Local UnitTests / Selenium passed.(❕)
• GitHub workflow CI (UnitTests / Selenium) passed.(❗)