chore: populate connectionlog count using a separate query (#18629)

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

coderd/database/dbauthz/setup_test.go

@@ -318,7 +318,7 @@ func hasEmptyResponse(values []reflect.Value) bool {
 			}
 		}
 
-		// Special case for int64, as it's the return type for count query.
+		// Special case for int64, as it's the return type for count queries.
 		if r.Kind() == reflect.Int64 {
 			if r.Int() == 0 {
 				return true