FE: Allow users to enable & disable epic colors in the epic board

Summary

With the implementation of color for epics in #7641 (closed), this issue is to address follow-up mentioned here. This setting should persist by board so that any teammate viewing it has a common view.

Noting this is the frontend issue, the backend issue is #382741 (closed).

Designs

Designs can be found here: #367306 (closed)

Issue blocked

This issue is blocked by the boards migration to Apollo.

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