Add loading variant for GlBadge

Proposal

To add isLoading prop to GlBadge component

Example

<gl-badge :is-loading="isLoading" variant="info">Validating...</gl-badge>

Above code should display a badge with spinner:

loader

Constraints

• This cannot be used in conjunction with the icon prop

Why

This should help users to avoid customizing the default slot to add a spinner