Refactor `vmseries` module

[migara]

The current vmseries module creates multiple firewalls, we need to move towards a singleton pattern similar to Azure modules.

Acceptance criteria

• Refactor input variables to accept parameters for a single VM-Series instance
• Refactor output variables to output related to a single instance
• Can deploy multiple instances using for_each at the module level
• Documentation is updated

[migara]

New PR for this issue #165