Optimize: Update obj func

[Tom-Szendrey]

Description:

• Clean - update many of the loose strings to enums as we know what they are expected to be.
• Fix - Since we have added relative weights using start_time_param_value would break our objective function. This was written with the assumption that length of x === length of interventions but this is not the case when we provide start_time_param_value as it will increase interventions by 1 and x by 2

Testing:

Run optimizes that do not include start_time_param_value -> Should pass as before
Run optimizes that do include start_time_param_value -> Should now pass

Example: while running with very minimal iterations and function eval (1-3, 1-3) we expect the result to be at or very close to the initial guess. We therefore expect to the resulting order to be: 1, 20, 0.2, 30
1st:

2nd:

3rd:

Result:

[blanchco]

didn't test, but looks good

[liunelson]

Looks good