Add Secure schemas version 15.0.0

What does this MR do?

Adds the latest version of the Secure schemas into GitLab Rails.

Related issue: #363134 (closed)

Background

Each GitLab Secure analyzer produces a JSON report that contains vulnerability findings to display on the Vulnerability Dashboard.

GitLab Secure schemas are used to ensure that reports produced by analyzers are able to be parsed successfully by GitLab Rails. Each JSON report indicates which version of the Secure schema it conforms to. When the report is parsed, the file is validated using the appropriate schema and will be rejected if it does not succeed.

A new version of the schema has been released, therefore in order to support analyzers using this version the new schema files must be included in the Rails codebase.

Reference

The git branch and associated MR was automatically created by https://gitlab.com/gitlab-org/security-products/security-report-schemas/-/jobs/3004078740.