Keep certain number of task executions in history

[ilayaperumalg]

Based on the changes addressed via #112, the entire history of task executions get deleted when launching a new task execution.

It would be nice to have at least a few task executions in the history to help enable the users debug the previous task executions. We also have some side effects such as the task execution logs are only available for the currently running execution.

This SO thread also has some more information: https://stackoverflow.com/questions/59433232/why-task-launcher-prunes-the-task-instance-history-every-time-a-new-task-instanc