Warning about invisible connections/variable in the Web UI

Hello,

Currently, you can define a new connection/variable in several ways.

• Metabase
• Environment variable
• Secret backend

However, only the connections defined with the Metabase are visible from the Web UI. This is surprising among users because a natural way to check connection/variable configuration is to use the Web UI, which may not show complete information. I would be happy if there was a warning stating that not all connections / variables are visible when the user has a configured secret backend or when the AIRFLOW__CONN_* /AIRFLOW__VAR_* environment variable is defined. This should appear above the list of connections/variables.

This change is intended to improve the user experience.

Best regards, Kamil Breguła