hydra-module.nix: More paranoid permissions on the data directory

Dependencies

• [2] T4DBPQOF hydra-module: Run hydra-init during hydra-init.service
• [3] D3MDJONY
• [4] ZYEFL36Q Ported/merged properties from the TUD configuration's hydra-module
• [5] KMPLMG7T hydra-module.nix: Cleanup

Change contents

• replacement in hydra-module.nix at line 183
  [3.927]→[3.252:287](∅→∅)
  − mkdir -p ${baseDir}/data
  [3.927]

  [2.100]
  + mkdir -m 0700 -p ${baseDir}/data