Allow Conditional Arbitrary Commands Flags

[terrorbyte]

It's been asked before if we can provide a --command flag to arbitrarily add user supplied strings in place of our payloads. Historically this wasn't trivial and we also have no way of indicating that a command could be used in-place. I'd like to add the ability for a C2 to indicate that a user supplied command could be used in place of one of our shell commands and support the ability to toggle on that flag.