Resolve the errors and warnings on epic board

What does this MR do and why?

There is one warning in console while loading epic board. It is due to mismatch in the graphql object of EpicListMetadata.

To resolve, sync the EpicListMetadata object in the epic board app.
On direct access of the epicsCount object, the following error was occurring on local

TypeError: Cannot assign to read only property

Use the cloneDeep to manipulate the epicsCount object in app/assets/javascripts/boards/stores/mutations.js instead of directly accessing it.

How to set up and validate locally

Load the epic board and check console.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.