Feature/add discovery vm flag

[SimOnPanw]

Description

Add vms command which corresponding to endpoint cloud/discovery/vms so that we can do something like pc discovery vms and get a table of all discovered VMs.

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes if appropriate.
• [ ] All new and existing tests passed.

[SimOnPanw]

Already merged into https://github.com/PaloAltoNetworks/prismacloud-cli/pull/144