Add Dag Run Conf to Run Backfill form

[bbovenzi]

Body

Creating a new Backfill is triggering many dag runs, so in our combined Trigger Run/Run Backfill modal we should keep the dag run conf available for both options and pass the conf value to the create backfill API request.

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.

[guan404ming]

Hi, I think I could help with this~

[bbovenzi]

Go for it!