Move basic/cron scheduling topic to "Authoring and Scheduling"

[ketozhang]

What do you see as an issue?

Basic information about scheduling is first introduced in DAGs and suddenly all available cron options are defined inDag Run section under Cron Presets.

This feel quite intuitive that DAG scheduling is part of DAG run.

Solving the problem

• Add a new subsection, Cron-based Scheduling to Authoring and Scheduling topic (diataxis)
• In DAGs add a sentence to send users to the Authoring and Scheduling to learn more about scheduling.
• Remove Cron Presets from DAG Run

Anything else

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct