Add guardrails for APP_NAME - certain functionality is dependent on there being a valid APP_NAME

[natsunlee]

APP_NAME is necessary for storing intermediate state/ctx files (in case of a job failure). When APP_NAME is blank/None, it will cause errors during save intervals.

Guardrails should be in place to check for the validity of APP_NAME prior to execution to ensure that a job that is setup for failure will not launch.