Update CD Procedure with Label info and new definition of CDs

There are two types of documentation at GitLab:

1. Controlled Documents: Formal policies, standards and procedures.

1. Uncontrolled Documents: Informal runbooks, certain handbook pages, guidelines, blog posts, templates, etc.

1. Controlled Documents: Change-controlled documents pertaining to policies, procedures, standards, or guidelines which are maintained for purposes of regulatory compliance, customer trust, and/or security best practices. Approval of changes is restricted to appropriate maintainers via the [CODEOWNERS](https://docs.gitlab.com/user/project/codeowners/) file.

1. Uncontrolled Documents: All other documents that do not need to be strictly change-controlled.

Everyone at GitLab is welcomed and encouraged to submit an MR to create or suggest changes to controlled documents at any time.

Controlled documents require a [handbook frontmatter attribute for controlled documents](http://handbook.gitlab.com/docs/frontmatter/) to classify them. This attribute also renders a warning header.

For Controlled Documents that are audit-facing, please add the following label under the frontmatter.

```{{< label name="Visibility: Audit" color="#E24329" >}}```

For Controlled Documents that are not audit-facing, please add the following label under the frontmatter.

```{{< label name="Visibility: Non-Audit" color="#428BCA" >}}```

If you need an example of how to do this, please review this page in the WebIDE.

### Review

Controlled documents are required to be reviewed and approved on at least an annual basis. Controlled documents may be updated ad-hoc as required by business operations. Changes must be approved by a code owner of the controlled document prior to merge.