Add support for using a "Patch" alias to determine what tasks to run upon commit.

Rather than always running every task in the evergreen file upon commit, I'd like to be able to specify which tasks and variants should be run similar to the Periodic Builds feature and Github Patch Definitions.

In my case, I have some tasks defined that should only be run by Periodic Builds. Currently, the only way to make some tasks not run is to have them isolated to a separate variant and set a large batch_time, which feels like a workaround to this feature.