Add generator service interval hours to vrmlogger

[mpvader]

Alex is expecting it.

The setting needs to be mirrored on the generator service. We do that to hide the difference between relay-based and other generators, so that it is logged on the DeviceInstance of the generator service rather than on com.victronenergy.settings.

TODO

• [x] Add path to dbus-generator-starter
• [x] Add to vrmlogger.