BE: Update the system notes for the color widget to be consistent with widget values

Summary

In !145934 (merged) we iterated on the new Color widget for Work Items to use color names rather than HEX values in the read-only state (these names are matched to tooltips we provide on the color picker options in edit state). The system notes are still referencing HEX values, which is a bit of a disconnect and would be better aligned to also use these color display names.

Additionally, we are using code elements to display the values in the system notes, which doesn't align to how we present these in the widget.

Proposal

• backend #451607: We create system notes in the backend and store them in the database as rendered 'Gitlab Flavoured Markdown' — currently making use of the 'color chip' feature: #bada55. We should update the values that are created and stored to use the new color display names we are using in the widget.
• frontend #478333: Change the visual styling to be similar to the widget values (and also other attributes we show in the system notes)

Design Reference

current	proposed