[5.8] Add option to create policy in art make:model command

[cwilby]

I regularly use policies so I figured this would be helpful - I'm not sure about the shorthand that I chose for this option as p is occupied by the pivot option.

...
['policy', 'pc', InputOption::VALUE_NONE, 'Create a new policy for the model'],
['pivot', 'p', InputOption::VALUE_NONE, 'Indicates if the generated model should be a custom intermediate table model'],
...

[bonzai]

#25787

[cwilby]

Closing - if @taylorotwell reconsiders he should use #25787.