Make badges in the header Pajamas compliant

What does this MR do and why?

This migrates badges in layouts/header/_default.html.haml to the shared gl_badge util. This affects the following badges:

• Canary badge
• Issue count
• MR total count
• Assigned MRs count
• Review requests count
• Todos count

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. To get the Next badge to show up, override the Canary condition like so:

   diff --git a/app/views/layouts/header/_default.html.haml b/app/views/layouts/header/_default.html.haml
   index 246a31f86c9..d24f8365cc1 100644
   --- a/app/views/layouts/header/_default.html.haml
   +++ b/app/views/layouts/header/_default.html.haml
   @@ -14,7 +14,7 @@
                - if logo_text.present?
                  %span.logo-text.d-none.d-lg-block.gl-ml-3
                    = logo_text
   -          - if Gitlab.com_and_canary?
   +          - if true
                = link_to Gitlab::Saas.canary_toggle_com_url, class: 'canary-badge bg-transparent', data: { qa_selector: 'canary_badge_link' }, target: :_blank, rel: 'noopener noreferrer' do
                  %span.gl-badge.gl-bg-green-500.gl-text-white.gl-rounded-pill.gl-font-weight-bold.gl-py-1
                    = _('Next')

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #344388 (closed)