Colocate service desk Haml code

What does this MR do and why?

This MR moves Haml templates that are only used on the service desk page to the same service_desk directory to colocate the code.

Some of these Haml templates used to be shared with the issues list and issues dashboard pages but these pages have now been converted to Vue and no longer use these templates.

Screenshots or screen recordings

How to set up and validate locally

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.