Document the GitLab Advisory Database

Problem to solve

We don't have any content on the GitLab documentation site that describes the GitLab Advisory Database.

Proposal

Incorporate relevant content from the following sources into a page that describes the GitLab Advisory Database. This could then be referenced from other features' documentation.

Who can address the issue

Anyone

Other links/references

Potential sources of information:

• https://advisories.gitlab.com/about/index.html
• https://about.gitlab.com/direction/secure/vulnerability-research/advisory-database/
• https://gitlab.com/gitlab-org/security-products/gemnasium-db