Front-end support for BigInt issue board total weight

What does this MR do and why?

This resolves #416218 (closed).

This transitions the front-end to use the new totalIssueWeight field that is a GraphQL::Types::BigInt (string). !124553 (merged)

This MR changes totalWeight to totalIssueWeight for issue boards only.

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This change should be unnoticeable in the UI, as the functionality or appearance should not change.

How to set up and validate locally

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