Default DagRun configuration

[casassg]

Description

It would nice to have the trigger UI pre-populated with default values for your dagrun configuration: https://airflow.apache.org/docs/stable/dag-run.html?highlight=params#using-ui

For that we need to add a new field to DAG that keeps the default conf for DAGRuns, serialize it and have it available on the Trigger UI.

This should allow user to more easily know what parameters/keys in config dictionary to expect.

Use case / motivation

Parameterize your DAG and change values easily on Trigger DAG UI.

Related Issues

#10587

[casassg]

I think we can activate dag_run_conf_overrides_params by default on master + #10839 (comment) it may be enough. Proposing change of default in #10587

[turbaszek]

@casassg is this issue still valid?

[casassg]

We can close it, with the changes I merged it may be good enough already.