This ticket should address the issue of how we raise errors when we fail to find a persistent sample. There are a few possible cases, for example:

1. no sample exists
2. sample was found but format is invalid
3. the samples collection is not clustered

Currently we return a Status when checking for a persistent sample. If it's an error status, we fall back to OTF sampling. For case 1 this is clearly correct, but cases 2 and 3 are situations where something has gone badly wrong with sample persistence. If they occur we would want to be notified through a BF/AF (i.e. tassert on those errors) but in production we likely want the customer's query to continue running since we have a viable fallback option.

Ideally we want the query to continue running but for us to be notified that the failure occurred.

We should also figure out if we should check that the createdAt field is consistent across pages in the sample.