Add Kubernetes and file operations steps mocks

[mahmoud-ashi]

Add mocks for steps from https://github.com/jenkinsci/kubernetes-plugin
Add mocks for steps from https://github.com/jenkinsci/file-operations-plugin
Add mock for libraryResource, lock, powershell
Fix mock for unstash step
Fix recently added mock for timeout with integer argument

[nre-ableton]

Please split 963ce57 up into 5 commits:

• One for the libraryResource mock
• One for the lock mock
• One for the powershell mock
• One for the timeout fix
• One for the unstash fix (which should probably include a corresponding fix for stash, since these steps are related).

That will make this PR much easier to review.

As for the mocks for Kubernetes and file-operations-plugins, please also split those into separate commits and make new PRs for each of them. I am personally disinclined to include mocks for such plugins in this library, since I believe that it should only cover base pipeline steps (otherwise, there is no limit to how much this library will grow, and it will get more difficult to maintain). However, I may be convinced otherwise, but we should have these discussions with other maintainers/contributors in a separate PR.

Thanks!