Adding global Stopping Strategy

[jessica-moylan]

Ax provides global stopping. This would be useful for a salutation in which a large number of trials are ran but at some point before the end of the number of trials, we stop improving and at which point we should quit optimizing.

This can be simplified to the following 3 steps:

1. RE(agent.optimize(10000)
2. We stop improvement at iteration 600
3. Plan exits/ quit optimization