Add a configurable workflow timeout to the create workflow API

[aburkleaux-amazon]

Having a workflow timeout can improve the robustness of applications built on MIE by forcing workflows that may be hung to terminate. Without a timeout, these workflows could consume all the available workflow slots (MAX_WORKFLOW_EXECUTIONS) and all subsequently added workflows execution requests will not run.

While there is no general timeout we could define for all possible MIE workflows, application owners can probably assign a reasonable timeout for their specific workflows and expected inputs.

1. Add a timeout option on the POST /workflow API
2. Set the timeout in the state machine created for the workflow