Add cvssV2 mapping in Snyk vulnerability parsing

### Current Behavior

Snyk parser maps and sets only cvssV3 information for either source NVD/SNYK.

### Proposed Behavior

It should parse cvssV2 as well in addition to cvssV3 and assign the values in object accordingly based on source priority.
Also, update the latest api version for Snyk and update the mapping if required.

### 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