You were using this plugin in some previous versions of Jenkins but you are not getting ssh plugin after upgrade in the newer versions.
This plugin is very useful if you want to run the script on remote host.
This is the solution for you.
Download hpi file
https://plugins.jenkins.io/ssh/#releases
and import it using
Manage Jenkins > Manage Plugins > Advanced > Upload
Restart Jenkins, the option will be there in the Build Environment and Build.
