Sync epic color with work item

What does this MR do and why?

Related to #440414 (closed)

Add support for syncing the epic's color with the associated work item.

Changes summary:

• When creating a legacy epic with a color value, add this value in widget_param and include these in the WorkItems::CreateService call so the synced work item is created with the given color.
• When updating an epic's color sync this value with the associated work item
• Creating and updating this color will not create system notes for the synced work item

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

create_epic_with_color

update_epic_color

create_epic_with_default_color

How to set up and validate locally

1. In rails console enable the experiment fully

   Feature.enable(:epic_creation_with_synced_work_item)

2. Visit a group and create a new epic with a set color
3. Visit the work items page for the group e.g. http://127.0.0.1:3000/groups/<group-path./-/work_items
4. A new work item should be present with the same attributes and color used for the epic
5. In the epic page update the color value in the sidebar and verify that the color is also updated for the synced work item
6. Create a new epic, this time leaving the default value for color, and verify that a synced work item is created with the epic default color.