Investigate how billing will be affected by switching to RepositoryInfo rpc

Follow up issue for discussion on how to proceed with switching from RepositorySize to RepositoryInfo.

We are concerned that rolling out the RepositoryInfo rpc could affect billing. We need to investigate how the new RepositoryInfo stats compare to the old RepositorySize stats.

Idea:

But if we want to be extra careful with this change, then we can run both RepositoryInfo and RepositorySize for percentage of calls and compare their values to ensure that there are no discrepancies.

Some pseudocode to describe the idea.

if Feature.enabled?(:use_repository_info_for_repository_size)
  bytes = gitaly_repository_client.repository_info.size

  (bytes.to_f / 1024 / 1024).round(2)
else
  kilobytes = gitaly_repository_client.repository_size

  repository_size_megabytes = (kilobytes.to_f / 1024).round(2)

  if Feature.enabled?(:test_repository_info_for_repository_size)
    bytes = gitaly_repository_client.repository_info.size

    repository_info_megabytes = (bytes.to_f / 1024 / 1024).round(2)

    if repository_info_megabytes != repository_size_megabytes
      log("Discrepancy between RepositorySize (#{repository_size_megabytes}) and RepositoryInfo (#{repository_info_megabytes})", project_id: project_id)
    end
  end

  repository_size_megabytes
end

We can run this version for 10% of calls (for example) and if there are no errors in logs for a week then it will be a confirmation that the feature flag is safe to enable.