Support passwordless / token-based authentication for external databases

### Current Behavior

- Dependency-Track requires a static username + password for external database connections.

- The application cannot acquire or refresh short-lived access tokens (e.g., Azure AD, AWS IAM, GCP IAM).

- This makes it impossible to use passwordless / identity-based database authentication models provided by cloud-managed PostgreSQL service

### Proposed Behavior

- Allow Dependency-Track to use token-based / passwordless database authentication (e.g., Azure AD, AWS IAM, GCP IAM).

- Support acquiring short-lived access tokens through the appropriate cloud identity libraries and using them for database connections.

- Handle token refresh so connections remain valid without requiring static passwords.

### Checklist

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