Add module to create Starboard vulnerabilities

For: gitlab-org/gitlab#330716 (closed)

This MR adds a new module named starboard_vulnerability which will read Starboard vulnerability reports from the Kubernetes cluster and create vulnerabilities in GitLab using an internal API. This allows us to scan container images for vulnerabilities while they are running inside a Kubernetes Cluster. See Cluster Image Scanning docs for more info.

Documentation for the changes in this MR: gitlab-org/gitlab!70308 (merged)