hydra-queue-runner: Limit concurrent database connections

Dependencies

• [2] NSBNNM77 Add hydra.conf option "nar_buffer_size" to configure memoryTokens limit
• [*] 24BMQDZA Start of single-process hydra-queue-runner

Change contents

• edit in src/hydra-queue-runner/hydra-queue-runner.cc at line 75
  [2.1421]

  [2.1421]
  + , dbPool(config->getIntOption("max_db_connections", 128))