Name or alias Shell Script Step (sh)

The `sh` step adds a "Shell Script" step in the Pipeline. However, there could be multiple such steps including steps from various plugins (e.g., Docker), which makes it hard to distinguish the steps. We should perhaps add an optional parameter to sh to specify a name or alias which would then appear in the pipeline steps.

e.g., the following can be the step for npm which would show as "Shell script: npm" in the pipeline view.

sh cmd:"npm install", name: "npm"