Fix issue rebalance banner

What does this MR do and why?

When issue rebalancing is in progress, we show a banner in issue lists and boards to notify the user that dragging of issues is temporarily disabled.

This fixes the banner so that:

1. We don't show 2 banners in the issue board page
2. We show the banner when the board is grouped by epics
3. We only show the banner in the issue list if "Manual" sort order is selected

How to set up and validate locally

1. Enable the block_issue_repositioning feature flag
2. Check issue boards and issue list with "Manual" sort order

MR acceptance checklist

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