Integrate handle_mailbox_soft_deleted.sh into 500-clean_mailboxes.inc.php

Closes #6445

See merge request !1733

Resolve "Show DKIM key in unsplit format"

Closes #6454

See merge request !1711

# Conflicts:
#   install/sql/incremental/upd_dev_collection.sql

Merge branch '6506-check-minimum-required-mysql-or-mariadb-version-during-installation-and-update' into 'develop'

Resolve "Check minimum required MySQL or MariaDB version during installation and update"

Closes #6506

See merge request ispconfig/ispconfig3!1743

Update upd_dev_collection.sql to remove regex mysql functions that will fail on older MySQL versions.

Resolve "Add menu.d directory support in all UI modules"

Closes #6508

See merge request ispconfig/ispconfig3!1746

#6509 Double_key_in_lang_file

See merge request ispconfig/ispconfig3!1745

Resolve "IPv6 only web server"

Closes #6477

See merge request !1705

6497 sorting for php versions

See merge request !1725

6467_clear_backup_fix

See merge request !1737

Grant dbmaster privileges on server_php, #6466

Closes #6466

See merge request !1742

Resolve "DNS zone import as user - wrong sys_groupid in dns_rr and dns_soa"

Closes #6504

See merge request !1741

PHP 8.x Misc fixes

See merge request !1726

Propose a basic editorconfig, #5522

Closes #5522

See merge request !1738

Add a util function running_on_master() to improve code readablility

See merge request !1735

Use a regular update to avoid waking the slaveserver

Closes #6453

See merge request !1734