Use Epic colours for display on the roadmap

What does this MR do and why?

Fetches the color and textColor properties from epics via GraphQL and uses the values for the roadmap progress bars

Screenshots or screen recordings

existing roadmap	default fallback	colourful roadmap (end goal)

How to set up and validate locally

You will need to connect to the database and update some epics to have a colour hex value as defined in app/assets/javascripts/vue_shared/components/color_select_dropdown/constants.js.

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.

Related to #7641 (closed)