Provide insights for bulk delete scenarios

This issue tracks providing an external user insight when [best practices](https://www.cockroachlabs.com/docs/stable/bulk-delete-data.html) are not followed when bulk deleting data. For instance, large DELETEs (e.g., millions of rows) should have an insight to break down the operation.

Jira issue: CRDB-26434

No source files, tests, or entry points are named. Start by reading the linked bulk-delete best practices and Jira issue CRDB-26434, then locate CockroachDB's existing insight mechanism and determine how bulk DELETE operations should be detected and reported; done means large operations produce the intended external insight.

Written by the indexing model from the issue text.