Resolve "User and group warnings during ISPConfig update"

Closes #6554

See merge request ispconfig/ispconfig3!1786

change adduser to usermod -a -G in install/dist/lib/gentoo.lib.php

See merge request !1787

there are some parts where a user is added to a group with "adduser" command.
changed "adduser" to "usermod -a -G" since there is no "adduser" in gentoo.

Merge branch '6549-switching-form-tabs-does-not-work-when-opening-website-form-from-dashboard' into 'develop'

Resolve "Switching form tabs does not work when opening website form from dashboard"

Closes #6549

See merge request !1783

6521_database_list_sort_on_dbuser_column

See merge request !1756

Fixed regex pattern for dkim_selector #6459

Closes #6459

See merge request !1769

6532_prevent_change_event_option

Closes #6532

See merge request !1763

Fix sorting of the database list by user, #6521

See merge request !1773

Add language_error_empty to the language files, #6495

See merge request !1774

Setting the language as a required field when creating a client

Closes #6495

See merge request !1719

Resolve "ISPConfig does not show red blinking dot when MySQL user password is changed"

Closes #1782 and #6550

See merge request !1782

Generalize the form title to be content aware, #6545

See merge request !1775

Resolve "Improve PHP 8.2 support"

Closes #6551

See merge request !1781

dovecot2.conf.master for gentoo

See merge request !1780

Resolve "Add support for Debian 12"

Closes #6527

See merge request !1777

In addition to !1719

Resolve "Dashboard Limit shows MB of Unlimited"

Closes #6544

See merge request !1772

Resolve "Account limit incorrectly informed in dashboard - ISPConfig 3.2.10"

Closes #6528

See merge request ispconfig/ispconfig3!1771

Merge branch '6533-domain-module-prevents-subdomains-to-be-added-for-domains-that-exist-as-website' into 'develop'

Resolve "Domain module prevents subdomains to be added for domains that exist as website"

Closes #6533

See merge request !1770

As the regex condition changed, the error message for invalid did too.
Lanuage files for en/de/es are now state the new rules for a valid selector.

Changed the regex pattern for dkim_selectors again. We now follow
the DKIMCore technical specification as stated on the website:

A selector is a string of no more than 63 lower-case alphanumeric characters (a-z or 0-9) followed by a period “.”, followed by another string of no more than 63 lower-case alphanumeric characters.