Merge branch '6522-dns-zones-can-not-be-added-with-wizard-when-domain-module-is-enabled' into 'develop'

Resolve "DNS zones can not be added with Wizard when domain module is enabled."

Closes #6522

See merge request ispconfig/ispconfig3!1757

Replace one more occurance of slave_zone_file_prefix, #6520

See merge request !1755

Fix mixed up version numbers in check_mysql_version

See merge request ispconfig/ispconfig3!1750

Improve verbosity when an error occurs during replication

Closes #6510

See merge request ispconfig/ispconfig3!1747

Only display a dashlet table if there is content for it, #6512

See merge request ispconfig/ispconfig3!1749

6516_help_system_message_sort_fix

See merge request ispconfig/ispconfig3!1752

Resolve "Error sending support message in ISPConfig panel"

Closes #6515

See merge request ispconfig/ispconfig3!1751

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

Closes #6445

See merge request ispconfig/ispconfig3!1733

Resolve "Show DKIM key in unsplit format"

Closes #6454

See merge request ispconfig/ispconfig3!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