Integrate description template list into page

What does this MR do and why?

Closes #463568 (closed)

Once this MR is closed, a followup will be raised to put the changes behind the work_items_alpha feature flag and merge the feature branch into master.

References

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MR acceptance checklist

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Screenshots or screen recordings

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Screen_Recording_2024-12-05_at_19.48.54

How to set up and validate locally

1. Visit any work item (or start creating a new one)
2. Click to edit the description, and notice the 'choose a template' listbox
3. Select one of the templates
4. Click 'Apply'
5. Check the template is applied to the description