This is the third PR for moving connection events out of the audit log.
This PR populates `count` on `ConnectionLogResponse` using a separate query, to preemptively mitigate the issue described in #17689. It's structurally identical to a portion of https://github.com/coder/coder/pull/18600, but for the connection log instead of the audit log.
Future PRs:
- Implement a table in the Web UI for viewing connection logs.
- Write a query to delete old events from the audit log, call it from dbpurge.
- Write documentation for the endpoint / feature