Add cvss-suite gem

What does this MR do and why?

We are working to integrate the security blog post automation into release-tools in gitlab-com/gl-infra&1073 (closed). The security-release-tools that currently generates the blog uses the cvss-suite gem to calculate some values and provide some helpers around the CVSS score. This MR introduces that gem to release-tools.

I've chosen to introduce the gem as it's own MR/commit to keep it separated from any code changes. I realize I could have done this as a separate commit in the MR that eventually uses it, but this way we can unblock future issues more easily.

Related to gitlab-com/gl-infra/delivery#19649 (closed)

Author Check-list

• [-] Has documentation been updated?