Move Sidekiq exporter logs to log/sidekiq_exporter.log

The Sidekiq exporter logs were mixing with the normal Sidekiq logs. In order to support structured logging in Sidekiq, we either need to split this data out or convert the exporter to produce structured logs. Since Sidekiq job processing is fundamentally different information from Web server traffic, it seems cleaner to move the metrics traffic into a separate file, where they can be parsed by a different filter if needed.

Relates to #20060 (closed)