Monitoring plugin to check if some packages are upgradeable (even if they are on hold).
First, install the required dependencies:

    apt install python3-apt

Then, create you own NRPE config file `/etc/nagios/nrpe.d/apt-custom.cfg` with something like this:

    command[asterisk_held_packages]=/usr/lib/nagios/plugins/check_apt_package --check-mark-for-keep asterisk asterisk-config asterisk-modules asterisk-mp3 asterisk-voicemail
    command[rocketchat_held_packages]=/usr/lib/nagios/plugins/check_apt_package --check-mark-for-keep rocketchat-server mongodb-org-server

