Dependency-Track Should Perform Update Check

### Current Behavior

Unlike many CI/CD servers (eg Jenkins, SonarQube, Nexus Reposiitory Manager), Dependency-Track does not inform the administrator when a new version of DT is available.

### Proposed Behavior

Dependency-Track should perform a regular check for latest version and clearly inform the administrator when an update is available.

If implemented in 4.12 and running 4.12, the MVP would be to inform that 4.12.1 or 4.13 is available. Ideally, the notification might separately also state that 5.0.0 is available... eg, inform of "minor/patch version update available" AND "major version update available"

The notification should also include a link (links) to release notes.

### 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