Make sources on identification stages orderable

### Is your feature request related to a problem?

We have multiple sources set up in Authentik and show a selection of them on identification stages. Some sources are more "important" for us than others and we want to basically render them in a defined order.

Currently there is no explicit ordering support in Authentik and the sources show up probably in the order they were created in the Authentik database.

### Describe the solution you'd like

We'd like to be able to assign a `order` number to each source (similar to the `order` for prompts or stages in a flow). Identification stage responses should then return the sources in the order of this `order` number.

### Describe alternatives that you've considered

Instead of a "global" `order` number per source this could also be done on the identification stage to sources relation level, i.e. a `order` number on the join model between identification stages and sources.

This would be more flexible but probably a bit more complex to implement.

### Additional context

_No response_