Fix : 'airflow connections test' failure by adding DB fallback

[anshuksi282-ksolves]

Description

This PR resolves an issue where the airflow connections test CLI command would fail with "Connection not found" or "conn_id isn't defined", even when the connection was clearly visible using airflow connections list.

The Issue:
Previously, connections_test relied solely on Connection.get_connection_from_secrets(args.conn_id). If the secrets backend failed to retrieve the connection (e.g., due to environment issues or Hook initialization failures), the CLI would exit with an error, ignoring the fact that the connection might exist in the Metastore Database.
In contrast, connections_list queries the database directly, creating a discrepancy between the two commands.

The Fix:
I have updated airflow/cli/commands/connection_command.py to implement a fallback mechanism:

1. It first attempts to retrieve the connection via the Secrets Backend (existing behavior).
2. If that fails (throws AirflowNotFoundException or returns None), it now explicitly checks the Database using create_session.
3. This ensures that if a connection exists in the DB, the CLI can still attempt to test it.

Related Issue

Closes #58567

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[potiuk]

That's not the right way of solving it.

Currently get_connection_from_secrets (and it's likely a misleading name but we have to keep it for compatibility) - will retrieve connection from configured secret backends and it will do it in the sequence the backends are configured.

Currently, the backends are always in predefined order but we have a change in progress #45931 that will allow to configure the order.

And connection list is different. connection list will only ever list connections that you have in database and nothing else, because there is no "enumeration" possibility when using the secrets backends.

So - I am not sure if there is anything to fix.

If you have backend configured and run connection.get and it fails with anything else than "NOT FOUND" - it should indeed fail, because it's possible that connection.get should return the connection from secret - not the one from the database.

So I think we should just close that issue.

[potiuk]

I am not even sure if that is the actual problem that was described in #58567