Stress-induced diffusion should be optional

[sravanpannala]

• PyBaMM version - 21.9:
• Python version - 3.9.7:

Describe the bug
Stress-induced diffusion should be option given to the user rather than enabling it by default when the "stress-driven' degradation model is activated.

To Reproduce
Steps to reproduce the behaviour:

1. Go to this file
2. Click on the fiel
3. Scroll down to def D_n_dimensional(self, sto, T)
4. See stress-induced diffusion modifier

Additional context
This part of the code should be optional and not hardcoded. Also, this code should not be in this file and rather in a submodel file.

[rtimms]

Yeah, we should pass options to the particle models and define the flux differently based on the options.