Made page content section stretch by default for all viewport sizes

[malincrist]

Problem

By default, the page content of the default layout stretches to the full width of the viewport only for "xl" screen size.

Solution

Apply "stretch" : "true" for all breakpoints (for the default developer portal content),

[github-actions]

Accessibility Insights Action: All applicable checks passed

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This scan used axe-core 4.3.2 with Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.75 Safari/537.36.