proposal: Windows support using SSH deploy key

[peaceiris]

cf. #86

[sdabhi23]

Hey @peaceiris I am trying to use this action on a windows environment on Actions. I am getting the following error:

Setup auth token
  [INFO] setup SSH deploy key
  "C:\Program Files\Git\usr\bin\chmod.exe" 700 C:\Users\runneradmin\.ssh
  [INFO] wrote C:\Users\runneradmin\.ssh\known_hosts
  "C:\Program Files\Git\usr\bin\chmod.exe" 600 C:\Users\runneradmin\.ssh\known_hosts
  [INFO] wrote C:\Users\runneradmin\.ssh\github
  "C:\Program Files\Git\usr\bin\chmod.exe" 600 C:\Users\runneradmin\.ssh\github
  [INFO] wrote C:\Users\runneradmin\.ssh\config
  "C:\Program Files\Git\usr\bin\chmod.exe" 600 C:\Users\runneradmin\.ssh\config
  C:\windows\system32\sc.exe config ssh-agent start=auto
  [SC] ChangeServiceConfig SUCCESS
  C:\windows\system32\sc.exe start ssh-agent
  
  SERVICE_NAME: ssh-agent 
          TYPE               : 10  WIN32_OWN_PROCESS  
          STATE              : 4  RUNNING 
                                  (STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
          WIN32_EXIT_CODE    : 0  (0x0)
          SERVICE_EXIT_CODE  : 0  (0x0)
          CHECKPOINT         : 0x0
          WAIT_HINT          : 0x0
          PID                : 2964
          FLAGS              : 
  C:\windows\System32\OpenSSH\ssh-add.exe C:\Users\runneradmin\.ssh\github
  Error connecting to agent: No such file or directory
  ##[error]Action failed with "The process 'C:\windows\System32\OpenSSH\ssh-add.exe' failed with exit code 2"

Workflow: https://github.com/sdabhi23/sdabhi23.github.io/actions/runs/158125330/workflow
Logs: https://github.com/sdabhi23/sdabhi23.github.io/runs/838257862?check_suite_focus=true

[peaceiris]

Thank you for reporting. This issue is still WIP.