o11y: problem ranges page doesn't load with large number of ranges

[ajstorm]

On the drt-large cluster, we currently have a large number of unavailable and under-replicated ranges:

In this state, the problem ranges page either loads very slowly (multiple minutes), hangs, or crashes the browser tab.

Jira issue: CRDB-37464

[dhartunian]

Problem Ranges is an Advanced Debug page so I'm downgrading this to a P-2 for now. We're going to have a bunch of work scoped in the next month or two that will provide a roadmap for getting DB Console stable for large clusters.