Add Supplement as functions

[Gonza10V]

Is your feature request related to a problem? Please describe.
When you want to test the response of the system to a pulse, you cant make it.

Describe the solution you'd like
A Supplement_function or Supplement.function style as a way to add supplements using functions of time

Describe alternatives you've considered
A different Class that does it instead of adding it to Supplement

Additional context
Function requested several times