Accomodate Observation Accuracy Experiment samples of size 10,000

[loarie]

Refactor Observation Accuracy Experiment method to distribute to validators to use Elastic Search directly rather than the API or otherwise speed up and modify to accommodate a sample of size 10,000 (vs 1,000).

Get results data methods may also have to be modified to limit the amount of data returned

Loading icon on https://github.com/inaturalist/inaturalist/blob/main/app/views/observation_accuracy_experiments/show.html.haml would already help indicate to users that the page is loading and will be necessary if the page slows down appreciably

• [x] Only include up to 500 observations in URLs
• [x] Use ES to speed up validator candidate selection
• [x] Use ES to speed up fetching sample obs continent metadata
• [x] Use ES to speed up fetching sample obs descendant count metadata
• [x] Show spinner on observation_accuracy_experiments/show until loaded

[loarie]

Work in progress on this branch https://github.com/inaturalist/inaturalist/tree/scale-observation-accuracy-experiment