Manually create L4D2 manifest file due to issues with steam

[danny6167]

Valve botched some recent changes to the way anonymous dedicated server apps are handled.

L4D2 is one of the few that are still broken.
ref: GameServerManagers/LinuxGSM#4706

Description

Checklist for all submissions

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you tested and reviewed your changes with confidence that everything works?
• Did you branch your changes and PR from that branch and not from your master branch?
  • If not, why?:

• You verify that the start command applied does not use a shell script
  • If some script is needed then it is part of a current yolk or a PR to add one
• The egg was exported from the panel