More informative error extrapolation drive cycle

[brosaplanella]

At the moment, if a drive cycle starts at t=1 rather than t=0 it throws a rather uninformative error (see below)

The easiest way to address this would be:

• Give the interpolant a meaningful name at creation so at least it is clear which interpolant is causing the error

  PyBaMM/pybamm/experiment/step/_steps_util.py

  Lines 123 to 125 in e0bec2b

  	self.value = pybamm.Interpolant(
  	t, y, pybamm.t - pybamm.InputParameter("start time")
  	)

• (Optionally) Perform a check and if drive cycle starts at t>0 throw a different, more specific error (or assume it's zero until first provided value, but I personally think this is dangerous).
• Add somewhere in the docs that drive cycles must start at t=0, added to Improve documentation (ongoing) #3392 already.

[jeromtom]

Would Drive cycle start time be an apt name?

[brosaplanella]

Would Drive cycle start time be an apt name?

For the drive cycle name? I would call it something like "Current drive cycle" (or power/voltage whatever drives it).

[R-Yash]

@brosaplanella I want to work on this issue. Is it still open?

[brosaplanella]

@jeromtom are you working on it? Otherwise @R-Yash can take it

[jeromtom]

@brosaplanella, I had worked on this but could not commit the changes due to a fault in my environment setup.
@R-Yash, you can refer to the following to fix it.

[R-Yash]

Thanks @jeromtom