This argument is pretty useless, so let's remove it and let addons get
their config on their own.
Note that this is a breaking change, but as [per
docs](https://woodpecker-ci.org/docs/next/administration/addons/overview)
the addon implementation can change at any time.
As of #2520
Support to load new forges and agent backends at runtime using go's
plugin system. (https://pkg.go.dev/plugin)
I also added a simple example addon (a new forge which just prints log
statements), it should be removed later of course, but you can see an
example.
---------
Co-authored-by: Michalis Zampetakis <mzampetakis@gmail.com>
Co-authored-by: Anbraten <anton@ju60.de>
