Follow-up: Add logging to custom email address for Service Desk feature

The following discussion from !123681 (merged) should be addressed:

• @splattael started a discussion: (+3 comments)

  Suggestion It seems we are discarding the service response. Thoughts on logging a message in case of an error? 🤔

  I also wonder if we could provide a reason for every ServiceResponse error and use this reason to decide whether we've handled email verification or not.

  Something like:

          def handled_custom_email_address_verification?
            response = ::ServiceDesk::CustomEmailVerifications::UpdateService.new(
              project: project,
              current_user: nil,
              params: {
                mail: mail
              }
            ).execute
  
            return false if response.reason == :not_a_verification_subaddress
  
            if response.error?
              # Log error
            end
  
            true

  WDYT?

I basically wanted to add a round of logs before we release the feature.