Fixed Windows Compatibility (fix for #23)

[JannesStroehlein]

This is a fix for #23.
I added a check if the OP_CLI_PATH ends in ".exe" indictating a path to a Windows program. If that's the case /op will not be appended to the executable path. Any executables on Windows will have the ".exe" extension.

Testing done

Not yet completed.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue