Allow to specify the shell for which commands should be generated in the SPFx project upgrade report in the spfx project upgrade command.

spfx project upgrade --shell [shell]

• shell: shell for which upgrade commands should be generated. Available values: bash|powershell|cmd. Default bash

Currently, we're generating upgrade commands based on bash with commands such as cp which don't work in cmd on Windows. By allowing to specify the target shell, we'd make it easier for developers on all platforms to upgrade their SPFx projects.