Fix visual spacing between labels in work item widgets

What does this MR do and why?

Adjust some visual spacing between the labels and content in the work items attribute widgets.

• Adds some space between Label widget text label and the assigned labels.
• Changes the Labels widget to use flex for the label elements instead of margins, which eliminates the extra margin that was present at the end of assigned labels (bottom margin).
• Removes some extra padding between Dates widget text label and "Start" field.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

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

1. Go to a work item detail page (ex: a Task)
2. Ensure there are Labels added to it
3. Look at the spacing between the Labels widget text label and assigned labels
4. Look at the spacing between the Dates widget text label and "Start" field