Fleet: Use active airline from session rather from hidden field

[flymia]

When adding or editing an aircraft, we use the current airline ID from the blade template. This is not a nice way of determining the active airline.

We need to append the current airline id from the session variable to the validated array.

Maybe using this approach:

• https://stackoverflow.com/questions/70635866/how-to-add-data-to-validated-request-input-bag

[flymia]

For Fleet this is fixed in #30 - I will close this here, since this is only relevant as of now for the fleet overview.