Add confirm button variant and aria label to modal

What does this MR do and why?

This MR adds details to the modal in ee/app/views/groups/saml_group_links/_saml_group_link.html.haml that we're migrating to GlModal as part of &6854 (closed) so that the confirm button in the new modal will be a danger-variant Remove link button instead of the generic OK button.

Screenshots or screen recordings

feature flag disabled	Feature.enable(:bootstrap_confirmation_modals) only	Feature.enable(:bootstrap_confirmation_modals) + this MR
Screen_Recording_2022-02-17_at_12.05.37	Screen_Recording_2022-02-17_at_12.00.46	Screen_Recording_2022-02-17_at_12.16.41

How to set up and validate locally

1. to get access to the page, set up SAML group sync in your gdk OR modify this line:

    def authorize_admin_saml_group_links!
-      access_denied! unless can?(current_user, :admin_saml_group_links, group)
+      access_denied! unless true
    end

2. create/choose a group and navigate to http://gdk.test:3000/groups/[YOUR GROUP NAME]/-/saml_group_links (or if you set up SAML fully, you can navigate to the group and use the sidebar link Settings => SAML Group Links)
3. fill in the form to add a SAML group link, it should appear in the list below
4. click the Remove button next to the group to open the modal

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 #344210 (closed)