Fixed work item layout width

What does this MR do and why?

Currently, we're setting work item layout width with limit-container-width class, that limits the width to 1006px. However, on the issue page we're only limiting the width of the "content" container, and sidebar is not included in the calculation. On the work item page, we limit both content and sidebar to 1006px which results in much narrower content width.

This MR increases the limit to 1006px + 320px (sidebar width) to achieve the issue-like UI.

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. In rails console enable the work items beta feature flag

   Feature.enable(:work_items_beta)

2. Open any work item in full-window view (not modal)
3. Inspect the page and make sure container width is set to 1326px

Related issue: #453997 (closed)