Add throttle option to register_batch_process

[jjeaton]

Allow throttling of a batch process, for things like email notifications.

[zachwills]

@jjeaton did you have an idea of how you'd like to set this as a developer using the plugin? Was it something simple like throttle => 60, or did you have something more powerful in mind?

[jjeaton]

yep, basically a parameter for a value to pass to usleep in microseconds for it to pause in between processing

[daronspence]

@jjeaton did you ever find a solution here? What about adding in the sleep function call to the callback function itself?

[jjeaton]

@daronspence No solution as of yet, we haven't run into the use case ourselves yet. PRs always welcome :)