hydra-queue-runner: Allow concurrent notifications

Dependencies

• [2] IE2PRAQU hydra-queue-runner: Send build notifications
• [3] 7LWB2J2Z Periodically clear orphaned build steps
• [4] XV4AEKJC hydra-queue-runner: Handle status queries on the main thread
• [5] GS4BE6TB Asynchronously compress build logs
• [*] 24BMQDZA Start of single-process hydra-queue-runner

Change contents

• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 836
  [2.2763]→[2.2763:2823](∅→∅)
  − std::thread(&State::notificationSender, this).detach();
  [2.2763]

  [2.2823]
  + auto maxConcurrentNotifications = config->getIntOption("max-concurrent-notifications", 2);

  + for (uint64_t i = 0; i < maxConcurrentNotifications; ++i)

  + std::thread(&State::notificationSender, this).detach();