Support setting flags from the config file

[paulkitt]

Currently only the configuration for the hooks are in a separate config file. To hide webhook behind Nginx or activate Https the systemd service file at /lib/systemd/system/webhook.service has to be edited. So in case of an update of the webhook package eather mine or your edits to that service file are lost.

It would be great if it would be possible to configure the webhook server ether with a section in the hooks file or via a separate config file.

[moorereason]

ff looks like a good candidate for this.