Docs as PDF in Release section

### Current Behavior

Currently the Docs are only available online and for the most recent version.

### Proposed Behavior

Due to various regulatories we are forced to archive the docs of DT corresponding to the version in use. Since we have also to provide these docs to regulatory bodies for audit reasons, it would be really helpful if the docs would be available as PDF (or similar file).

### 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