feat(GlPopover): add support for a close button

• Integration MR: gitlab!78932 (merged)

What does this MR do?

This adds the ability to show a close button in GlPopover.

• Review app: http://1674-popover-close-button.64.227.120.153.nip.io/?path=/story/base-popover--with-close-button

Closes #1674 (closed)