Draft: Add documentation warning to Danger message

What does this MR do and why?

It is common for engineers to forget to document their feature changes. This adds a Danger warning that will be posted in every MR that has a type::feature label but does not make any changes to the documentation.

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MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.