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).

Implementation Details

We use updateEpicBoard mutation to update the board settings when we edit it from UI, currently it shows following options;

Current	Proposed

And we need to add a third checkbox update the checkbox UI as per #367306[Edit_board_modal.png]. The mutation already supports displayColors param in variables so once we add support for changing it, we should also start reading its value and hide/show colors on board based on its value.

Designs

Designs can be found here: #367306 (closed)

Issue blocked

This issue is blocked by the boards migration to Apollo.

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