Add a TaskBuilder method to modify the value for the runAfter part of the task's yaml

[David-M-IBM]

Currently there is no way to change the runAfter value of a task to have custom multiple, single, or no value, and it is always the one before it. This isn't always what you want in a pipeline, especially if you want certain tasks to run in parallel.

Adding a method to the TaskBuilder class to specify the runAfter value would solve the problem.

An example of what the main.ts section could look like:

.withTask(new TaskBuilder(this, "task-id")
      .specifyRunAfter(["array","of","task","ids"])
      .withName("task-name")
  )

An example of what the section of pipeline yaml could look like:

   - name: task-id
      runAfter:
        - array
        - of
        - task
        - ids
      taskRef:
        kind: Task
        name: task-name

[snehajais22]

Closed by #48