Add Compensation Workflow Pattern Example

[cicoyle]

Similar to this compensation workflow pattern example in the java sdk, we should have an example of how to do compensation logic in php.

Here is the example code.
Here is the readme for it.
Here are the docs for it.

We can still improve it after the fact, but we should have a clear example how users can implement this workflow pattern.

We can eventually add something like the following, but in php:

ctx.CallActivityWithCompensation(ctx, 
        "BookFlight", nil,
        "CancelFlight", nil)
if err != nil {
        // Compensate
        return err
    }

The ask for now is to simply show users how they can implement this pattern in an example.

RELEASE NOTE:
ADD Workflow Compensation Pattern Example