Planning to host the data classification in a yaml file in the handbook.

Why is this change being made?

I am adding this file to the repo because I am planning to host the data classification index in a yaml file in the handbook. The handbook will point to this file, similar to the tech stack details handbook page pulls from the Tech Stack yaml file.

The goal here is to enable better version control of the Data Classification index, to enable greater visibility as the current one is limited to GitLab employees, and to ensure everyone can contribute to the index.

Closes https://gitlab.com/gitlab-com/gl-security/security-assurance/governance/security-assurance-automation/-/issues/141+

Author Checklist

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