Option to hide other observations on maps (Observation Detail page, Identify)

Thoughts on merging these two requests and expanding this one to include the Identify page? They seem pretty similar. Like @jdmore said, I think it’s the observation pinpoints on the map, not the map itself, that makes loading slow.

https://forum.inaturalist.org/t/option-for-maps-off-browsing/2749 (cc: @er1kksen)