hydra-queue-runner: Allow multiple concurrent daemon connections

Dependencies

• [2] IKJBYIGY Update to reflect BinaryCacheStore changes
• [3] V2UCCYN3 hydra-queue-runner: Get store mode configuration from hydra.conf
• [4] B2L4T3X6 Sync with Nix
• [5] NSBNNM77 Add hydra.conf option "nar_buffer_size" to configure memoryTokens limit
• [6] SOB276BA Keep some statistics for the binary cache stores
• [7] K5G5GZY7 Guard against concurrent invocations of hydra-queue-runner
• [*] 24BMQDZA Start of single-process hydra-queue-runner

Change contents

• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 782
  [3.828]→[2.234:264](∅→∅)
  − localStore = openStore();
  [3.828]

  [2.299]
  + Store::Params localParams;

  + localParams["max-connections"] = "16";

  + localStore = openStore(getEnv("NIX_REMOTE"), localParams);