Resolve "MR Changes Cog dropdown checkboxes alignment broken"

What does this MR do?

For #323313 (closed)

A recent change to the GlFormCheckbox layout uses padding to leave space for the actual checkbox element.

This has broken anything that used padding utility classes to position the component.

This MR switches to left margin instead of left padding to recreate the previous layout.

Screenshots (strongly suggested)

Before	After

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