Migrate contribution checkbox to Pajamas component

app/views/projects/merge_requests/_form.html.haml

-= form_for [@project, @merge_request],
+= gitlab_ui_form_for [@project, @merge_request],
            html: { class: 'merge-request-form common-note-form js-requires-input js-quick-submit' } do |f|
   = render 'shared/issuable/form', f: f, issuable: @merge_request, presenter: @mr_presenter

app/views/projects/merge_requests/creations/_new_submit.html.haml

 %h3.page-title
   = _('New merge request')
-= form_for [@project, @merge_request], html: { class: 'merge-request-form common-note-form js-requires-input js-quick-submit' } do |f|
+= gitlab_ui_form_for [@project, @merge_request], html: { class: 'merge-request-form common-note-form js-requires-input js-quick-submit' } do |f|
   = render 'shared/issuable/form', f: f, issuable: @merge_request, commits: @commits, presenter: @mr_presenter
   = f.hidden_field :source_project_id
   = f.hidden_field :source_branch

app/views/shared/issuable/form/_contribution.html.haml

 - issuable = local_assigns.fetch(:issuable)
 - form = local_assigns.fetch(:form)
+- contribution_help_link = help_page_path('user/project/merge_requests/allow_collaboration')
+- contribution_help_link_start = '<a href="%{url}" target="_blank" rel="noopener noreferrer">'.html_safe % { url: contribution_help_link }
 
 - return unless issuable.is_a?(MergeRequest)
 - return unless issuable.for_fork?
@@ -11,10 +13,7 @@
   %label.col-form-label.col-sm-2
     = _('Contribution')
   .col-sm-10
-    .form-check.gl-mt-2
-      = form.check_box :allow_collaboration, disabled: !issuable.can_allow_collaboration?(current_user), class: 'form-check-input'
-      = form.label :allow_collaboration, class: 'form-check-label' do
-        = _('Allow commits from members who can merge to the target branch.')
-        = link_to 'About this feature', help_page_path('user/project/merge_requests/allow_collaboration'), target: '_blank', rel: 'noopener noreferrer nofollow'
-        .form-text.text-muted
-          = allow_collaboration_unavailable_reason(issuable)
+    = form.gitlab_ui_checkbox_component :allow_collaboration,
+      _('Allow commits from members who can merge to the target branch. %{link_start}About this feature.%{link_end}').html_safe % { link_start: contribution_help_link_start, link_end: '</a>'.html_safe },
+      checkbox_options: { disabled: !issuable.can_allow_collaboration?(current_user) },
+      help_text: allow_collaboration_unavailable_reason(issuable)

app/views/shared/issuable/form/_metadata.html.haml

@@ -17,9 +17,8 @@
 - if issuable.respond_to?(:confidential) && can?(current_user, :set_confidentiality, issuable)
   .form-group.row
     .offset-sm-2.col-sm-10
-      .form-check
-        = form.gitlab_ui_checkbox_component :confidential,
-        s_('This issue is confidential and should only be visible to team members with at least Reporter access.')
+      = form.gitlab_ui_checkbox_component :confidential,
+        _('This issue is confidential and should only be visible to team members with at least Reporter access.')
 
 - if can?(current_user, :"set_#{issuable.to_ability_name}_metadata", issuable)
   %hr

locale/gitlab.pot

@@ -3651,7 +3651,7 @@ msgstr ""
 msgid "Allow access to the following IP addresses"
 msgstr ""
 
-msgid "Allow commits from members who can merge to the target branch."
+msgid "Allow commits from members who can merge to the target branch. %{link_start}About this feature.%{link_end}"
 msgstr ""
 
 msgid "Allow group owners to manage LDAP-related settings"