CLI support for an optional ,interval for the guest profiler, to match wasmtime

[katef]

In #301 support for guest profiling was added. This corresponds to an equivalent CLI flag in wasmtime introduced in bytecodealliance/wasmtime#6362 (and documented in bytecodealliance/wasmtime#6393).

We have no way to control the profiling interval for Viceroy:

Viceroy: --profile=guest[,path]
Wasmtime: --profile=guest[,path[,interval]]

This ticket is to add the optional ,interval part, just like wasmtime has.