v5: Index USR_USERNAME_IDX should include column type

### Current Behavior

With V5, the OIDCUSER and MANAGEDUSER tables were consolidated into the USER table and discriminated by the `type` column. However, the current index USER_USERNAME_IDX does not include the `type` column, making a collision possible between two unrelated object types.

### Steps to Reproduce

1. Create a blank v5 database
2. Create an OIDC username `admin`
3. Attempt to login with OIDC username `admin`

### Expected Behavior

Unique index should include columns `username` and `type`.

### Dependency-Track Version

5.x

### Browser

Google Chrome

### Checklist

- [x] I have read and understand the [contributing guidelines](https://github.com/DependencyTrack/dependency-track/blob/main/CONTRIBUTING.md#filing-issues)
- [x] I have checked the [existing issues](https://github.com/DependencyTrack/dependency-track/issues) for whether this defect was already reported