Attributes field in application

**Is your feature request related to a problem? Please describe.**
We're migrating a bulk of applications, and those have some arbitrary pieces of information that we'd like to authentik-ify gradually (Like entitlements, special property mappings, user/group bindings, etc.)

But there's no place for arbitrary data on application, like it would be on User/Group/Entitlement

**Describe the solution you'd like**
Have the same `attributes` field as with User / Group (including filters) in the application object.

**Describe alternatives you've considered**
Keeping a parallel data store tracking these extra bits of information

**Additional context**
N/A