ui: index details statements list req interval is too short

The call to fetch statements using an index in the index details is only 100ms. While there are guardrails in place in the request body to ensure we only fetch new data, this interval should be increased. The conditions for which we fetch new data also need to be verified, as we've seen this call get spammed on some clusters.

https://github.com/cockroachdb/cockroach/blob/2e787c02c0d399c575ae6dde5c7a75723f4ba7fc/pkg/ui/workspaces/cluster-ui/src/indexDetailsPage/indexDetailsPage.tsx#L190-L192

Jira issue: CRDB-47139