Add support for on_conflict: :log for UntilExecuting lock

[lairtonlelis]

When setting a worker with on_conflict: log configuration and the until_executing or the until_and_while_executing locks, like the worker below:

class ExampleWorker
  include Sidekiq::Worker

  sidekiq_options lock: :until_and_while_executing,
                         on_conflict: :log

  def perform(fund_id)
    puts 'performed...'
  end
end

the logs are misleading, showing a message like this:

2019-04-29T16:54:27.402Z 1 TID-oxrddqzzp SidekiqUniqueJobs::Client::Middleware DIG-uniquejobs:d7e6681a477cc2e705a03b6628b093c6 INFO: skipping job with id (a7540e0b85eaed075b877362) because unique_digest: (uniquejobs:d7e6681a477cc2e705a03b6628b093c6) already exists

But the job is not skipped and gets executed by the sidekiq worker.

A possible solution would be to add support for on_conflict: :log configuration for the until_executing and until_and_while_executing locks, as this is not currently supported (shown here).

[mhenrixon]

Duplicate of #402

The log strategy is supported but since the server locks (the locks that create a unique lock as the server middleware is called) it isn't really that useful. That's why I decided to split the configuration to allow separate conflict strategies for the client and server.