Write a tool to find accounts with large numbers of failed validations and no successful issuances

[jsha]

As discussed in https://community.letsencrypt.org/t/possible-new-feature-paused-acme-accounts/148364, I'd like to add a "paused accounts" feature. Part of the motivation is that we have a large number of clients that fail validation repeatedly, and I expect that this technique would significantly reduce the load from these clients. The first step is to write a tool that will query our database for accounts with a moderate number of failed validations (5 in the last week), plus zero successful issuance in the last 180 days.

Given that list, it should also scan the authz2 table to determine how many failed validation attempts would hypothetically have been eliminated if these accounts were paused: both as a total count, and as a fraction of failed validations and a fraction of validations overall.

[aarongable]

This idea was completed by #7763