Improve DAG Factory nomenclature consistencies

[tatiana]

This feedback was reported by Karen Braganza on DAG Factory 0.19.0:

Some parameter names do not match between Airflow and DAG Factory (example: schedule vs schedule_interval or execution_timeout vs execution_timeout_secs). This can be confusing without comprehensive documentation. I often had to read through the code to determine correct parameter names, which defeats the purpose of DAG factory for people unfamiliar with Python.

This confusion is exacerbated by inconsistencies in nomenclature within DAG factory itself. Example:

• retry_delay_sec and dagrun_timeout_sec end with sec
• On the other hand, execution_timeout_secs and sla_secs end with secs.
• There is an extra ‘s’ at the end of execution_timeout_secs and sla_secs. These parameter names should be consistent.

I believe some of the inconsistencies may have been introduced for backwards compatibility since DAG Factory has historically supported many versions of Airflow, including 1.x. That said, I agree with Karen we should review and make these more consistent.