Expand observer package to include a rain detector

Rain drops on the dome cause a large number of false positives.
Maybe see if we can detect when it rains so as to turn off the tracker for the rain period.

https://stackoverflow.com/questions/74891364/detect-drops-of-water-using-opencv

Start by locating and reading the observer package, then review the linked OpenCV discussion about detecting water drops. Define how rain detection should identify rain and how the tracker should be disabled for that period; completion is a detector integrated with the observer package and verified against the false positives described.

Written by the indexing model from the issue text.