Add a structured `sidekiq_client.log` file for job related messages for sidekiq client

Add a SidekiqClientLogger to write job related events that happen on the client-side of sidekiq and configure Sidekiq.logger to write to that logger on the client. We could then ingest sidekiq_client.log in (#201 (closed)) into the sidekiq index, so we have a single index where we can aggregate job information.

This means that developers can use Sidekiq.logger to write job related information, if this is done within a a job running on sidekiq server, this will go to STDOUT of sidekiq itself. When this is done on the client, the message would go to the new sidekiq_client.log.