[FEAT]: Include a prompt in the prompt dropdown of "Edit model" operator for adding time property to the model

[liunelson]

Is your feature request related to a problem? Please describe.

"Create model from equations" operator produces models without a time property.

We can add it to a model using "Edit model" with this MIRA command:

model.time = Time(name = 't', units = Unit(expression=sympy.Symbol('day')))

Add a prompt to the prompt dropdown to do this for people who don't know MIRA

Specify the time unit of the model to be "day"