fix: load attachment images more reliably

[achou11]

Fixes #447

The following places have been updated as follows:

1. Observations list: used to only render previews. Now we fallback to thumbnails if previews cannot be loaded.
2. Observation details: used to only render originals. Now we fallback to previews if originals cannot be loaded, and then thumbnails if previews cannot be loaded.
3. Observation attachment: used to only render originals. Now we render the variant that matches the variant param in the URL. Note that we DO NOT try to render other variants as fallbacks. We can consider doing that or redirecting to the relevant URLs if desired, but in most cases this won't be necessary since navigation links to this page are only available based on the presence of the relevant variant.

For all of these, I've also improved the error handling so that there are clearer logs in Sentry. Before, we'd get reports about the image load error event from SuspenseImage, which were not very informative e.g. title would be something like AsyncContextStack.withScope and message like Event (type=error) captured as exception. Now we provide a more semantic log e.g. Failed to load original image along with a payload about the attachment/blob that can be found in the Additional Data section on Sentry.