Add position offset options

Currently we are able to set the position of the notification with anchor, but I want to be more specific about where the notification appears. If there was an option such as x-offset/y-offset this would enable me to do such.

I specifically want my notifications to appear over my bar on top so I'd want to do a negative y-offset.

No file or test is named in the issue. Start by tracing the existing anchor-based notification positioning and the configuration or option parsing entry point; done means configurable x/y offsets work, including a negative y-offset for notifications above the bar.

Written by the indexing model from the issue text.