Kea fails to start with log4cplus compiled without implicit initialization

Describe the bug

Log4cplus introduced new build option to disable implicit initialization during startup in 2.0.4 (https://sourceforge.net/p/log4cplus/news/2019/04/v204/):

--disable-implicit-initialization

With this option enabled Kea's binaries won't start:

# ./kea-dhcp4 -c /etc/kea/kea-dhcp4.conf
kea-dhcp4: Fatal error during start up: log4cplus is not initialized and implicit initialization is turned off

Particularly latest log4cplus package in Alpine Linux is compiled with this option. As a result one can't use Kea with Alpine without building it from sources (https://bugs.alpinelinux.org/issues/10480).

To Reproduce

Steps to reproduce the behavior:

Configure and build log4cplus version 2.0.4 with --disable-implicit-initialization option;
Build Kea using that log4cplus library;
Try to start Kea server

# ./kea-dhcp4 -c /etc/kea/kea-dhcp4.conf
kea-dhcp4: Fatal error during start up: log4cplus is not initialized and implicit initialization is turned off

Expected behavior

# ./kea-dhcp4 -c /etc/kea/kea-dhcp4.conf
INFO  [kea-dhcp4.dhcp4/14122] DHCP4_STARTING Kea DHCPv4 server version 1.5.0-git starting

Environment:

Kea version: 1.5.0;
OS: Any;
Log4cplus with --disable-implicit-initialization;

Describe the solution you'd like

Explicitly initialize log4cplus in Kea.

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