[4.2] Switching nightly builds from Jenkins to Drone

[Hackwar]

This implements the nightly builds for 4.2-dev for Drone.

[zero-24]

Please also include a notification on any issue that comes up. in the past (with Jenkins) also also had a notification when it was successfull, not sure whether we still need that. We also need to have a way to manually trigger this right after the releases.

[wilsonge]

Also needs to be manually triggerable post release (as part of the release checklist https://github.com/joomla/joomla-cms/blob/4.1-dev/build/release-checklist.md )

[zero-24]

@HLeithner we are still missing an 'it run successfull' notification right? not that we have to have that forever but it might help to be sure it run and deployed successfull right?

[Hackwar]

The notification is implemented, but somehow is not always executed. The notifications can be improved by improving the notify script in the packager docker image.